HRD Conformance Tests On OLS

ABSTRACT

A video coding mechanism is disclosed. The mechanism includes encoding a bitstream comprising one or more output layer sets (OLSs). A video parameter set (VPS) specifying the OLS is also encoded into the bitstream. A set of bitstream conformance tests are performed at each operation point (OP) of each OLS, as specified by the VPS, to test each OP for conformance. The bitstream is stored for communication toward a decoder.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of International ApplicationNo. PCT/US2020/049719, filed Sep. 8, 2020 by Ye-Kui Wang, and titled“HRD Conformance Tests On OLS,” which claims the benefit of U.S.Provisional Patent Application No. 62/905,244 filed Sep. 24, 2019 byYe-Kui Wang, and titled “Hypothetical Reference Decoder (HRD) forMulti-Layer Video Bitstreams,” which are hereby incorporated byreference.

TECHNICAL FIELD

The present disclosure is generally related to video coding, and isspecifically related to hypothetical reference decoder (HRD) parameterchanges to support efficient encoding and/or conformance testing ofmulti-layer bitstreams.

BACKGROUND

The amount of video data needed to depict even a relatively short videocan be substantial, which may result in difficulties when the data is tobe streamed or otherwise communicated across a communications networkwith limited bandwidth capacity. Thus, video data is generallycompressed before being communicated across modern daytelecommunications networks. The size of a video could also be an issuewhen the video is stored on a storage device because memory resourcesmay be limited. Video compression devices often use software and/orhardware at the source to code the video data prior to transmission orstorage, thereby decreasing the quantity of data needed to representdigital video images. The compressed data is then received at thedestination by a video decompression device that decodes the video data.With limited network resources and ever increasing demands of highervideo quality, improved compression and decompression techniques thatimprove compression ratio with little to no sacrifice in image qualityare desirable.

SUMMARY

In an embodiment, the disclosure includes a method implemented by adecoder, the method comprising: receiving, by a receiver of the decoder,a bitstream comprising one or more output layer sets (OLSs) and a videoparameter set (VPS) specifying the OLSs, wherein the bitstream has beenchecked by a set of bitstream conformance tests that test conformance ofeach operation point (OP) of each OLS specified by the VPS; anddecoding, by a processor of the decoder, a picture from the OLSs.

Video coding systems employ various conformance tests to ensure abitstream is decodable by a decoder. For example, a conformance checkmay include testing the entire bitstream for conformance, then testingeach layer of the bitstream for conformance, and finally checkingpotential decodable outputs for conformance. In order to implementconformance checks, corresponding parameters are included in thebitstream. A hypothetical reference decoder (HRD) can read theparameters and perform the tests. A video may include many layers andmany different OLSs. Upon request, the encoder transmits one or morelayers of a selected OLS. For example, the encoder may transmit the bestlayer(s) from an OLS that can be supported by the current networkbandwidth. A problem with this approach is that a significant number oflayers are tested, but not actually transmitted to the decoder. However,the parameters to support such testing may still be included in thebitstream, which needlessly increases the bitstream size. The presentexample includes a mechanism to apply bitstream conformance tests toeach OLS only. In this way, the entire bitstream, each layer, and thedecodable outputs are collectively tested when the corresponding OLS istested. Therefore, the number of conformance tests is reduced, whichreduces processor and memory resource usage at the encoder. Further,reducing the number of conformance tests may reduce the number ofassociated parameters included in the bitstream. This decreasesbitstream size, and hence reduces processor, memory, and/or networkresource utilization at both the encoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the set of bitstream conformance tests areperformed by a hypothetical reference decoder (HRD) operating on anencoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the VPS includes a total number of outputlayer sets minus one (numoutput_layer _sets_minus1) plus one thatspecifies a total number of OLSs specified by the VPS.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein each OP is selected as an OP under test(targetOp) based on a target OLS with an OP OLS index (opOlsIdx) and ahighest OP temporal identifier value (opTid).

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein each OLS is a set of layers for which oneor more of the layers are specified as output layers.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the VPS includes a general HRD parameters(general_hrd_parameters) syntax structure that provides HRD parametersthat apply to all OLSs specified by the VPS.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein a presence of the HRD parameters in thebitstream indicates the decoder is capable of decoding the bitstreamaccording to a delivery schedule.

In an embodiment, the disclosure includes a method implemented by anencoder, the method comprising: encoding, by a processor of the encoder,a bitstream comprising one or more OLSs; encoding into the bitstream, bythe processor, a VPS specifying the OLSs; and performing, by theprocessor, a set of bitstream conformance tests at each OP of each OLS,as specified by the VPS, to test each OP for conformance.

Video coding systems employ various conformance tests to ensure abitstream is decodable by a decoder. For example, a conformance checkmay include testing the entire bitstream for conformance, then testingeach layer of the bitstream for conformance, and finally checkingpotential decodable outputs for conformance. In order to implementconformance checks, corresponding parameters are included in thebitstream. A hypothetical reference decoder (HRD) can read theparameters and perform the tests. A video may include many layers andmany different OLSs. Upon request, the encoder transmits one or morelayers of a selected OLS. For example, the encoder may transmit the bestlayer(s) from an OLS that can be supported by the current networkbandwidth. A problem with this approach is that a significant number oflayers are tested, but not actually transmitted to the decoder. However,the parameters to support such testing may still be included in thebitstream, which needlessly increases the bitstream size. The presentexample includes a mechanism to apply bitstream conformance tests toeach OLS only. In this way, the entire bitstream, each layer, and thedecodable outputs are collectively tested when the corresponding OLS istested. Therefore, the number of conformance tests is reduced, whichreduces processor and memory resource usage at the encoder. Further,reducing the number of conformance tests may reduce the number ofassociated parameters included in the bitstream. This decreasesbitstream size, and hence reduces processor, memory, and/or networkresource utilization at both the encoder and the decoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the set of bitstream conformance tests areperformed by a HRD operating on the processor.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the VPS includes anum_output_layer_sets_minus1 plus one that specifies a total number ofOLSs specified by the VPS.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, further comprising selecting, by the processor,each OP as an targetOp by selecting a target OLS with an opOlsIdx and ahighest opTid.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein each OLS is a set of layers for which oneor more of the layers are specified as output layers.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the VPS includes a general_hrd_parameterssyntax structure that provides HRD parameters that apply to all OLSsspecified by the VPS.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein a presence of the HRD parameters in thebitstream indicates a decoder is capable of decoding the bitstreamaccording to a delivery schedule.

In an embodiment, the disclosure includes a video coding devicecomprising: a processor, a receiver coupled to the processor, a memorycoupled to the processor, and a transmitter coupled to the processor,wherein the processor, receiver, memory, and transmitter are configuredto perform the method of any of the preceding aspects.

In an embodiment, the disclosure includes a non-transitory computerreadable medium comprising a computer program product for use by a videocoding device, the computer program product comprising computerexecutable instructions stored on the non-transitory computer readablemedium such that when executed by a processor cause the video codingdevice to perform the method of any of the preceding aspects.

In an embodiment, the disclosure includes a decoder comprising: areceiving means for receiving a bitstream comprising one or more OLSsand a VPS specifying the OLSs, wherein the bitstream has been checked bya set of bitstream conformance tests that test conformance of each OP ofeach OLS specified by the VPS; a decoding means for decoding a picturefrom the OLSs; and a forwarding means for forwarding the picture fordisplay as part of a decoded video sequence.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the decoder is further configured toperform the method of any of the preceding aspects.

In an embodiment, the disclosure includes an encoder comprising: anencoding means for: encoding a bitstream comprising one or more OLSs;and encoding into the bitstream a VPS specifying the OLSs; a HRD meansfor performing a set of bitstream conformance tests at each OP of eachOLS, as specified by the VPS, to test each OP for conformance; and astoring means for storing the bitstream for communication toward adecoder.

Optionally, in any of the preceding aspects, another implementation ofthe aspect provides, wherein the encoder is further configured toperform the method of any of the preceding aspects.

For the purpose of clarity, any one of the foregoing embodiments may becombined with any one or more of the other foregoing embodiments tocreate a new embodiment within the scope of the present disclosure.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, taken in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is a flowchart of an example method of coding a video signal.

FIG. 2 is a schematic diagram of an example coding and decoding (codec)system for video coding.

FIG. 3 is a schematic diagram illustrating an example video encoder.

FIG. 4 is a schematic diagram illustrating an example video decoder.

FIG. 5 is a schematic diagram illustrating an example hypotheticalreference decoder (HRD).

FIG. 6 is a schematic diagram illustrating an example multi-layer videosequence configured for inter-layer prediction.

FIG. 7 is a schematic diagram illustrating an example multi-layer videosequence configured for temporal scalability.

FIG. 8 is a schematic diagram illustrating an example bitstream.

FIG. 9 is a schematic diagram of an example video coding device.

FIG. 10 is a flowchart of an example method of encoding a video sequenceto support performance of bitstream conformance tests for an OLS.

FIG. 11 is a flowchart of an example method of decoding a video sequencethat was subjected to bitstream conformance tests for an OLS.

FIG. 12 is a schematic diagram of an example system for coding a videosequence to support performance of bitstream conformance tests for anOLS.

DETAILED DESCRIPTION

It should be understood at the outset that although an illustrativeimplementation of one or more embodiments are provided below, thedisclosed systems and/or methods may be implemented using any number oftechniques, whether currently known or in existence. The disclosureshould in no way be limited to the illustrative implementations,drawings, and techniques illustrated below, including the exemplarydesigns and implementations illustrated and described herein, but may bemodified within the scope of the appended claims along with their fullscope of equivalents.

The following terms are defined as follows unless used in a contrarycontext herein. Specifically, the following definitions are intended toprovide additional clarity to the present disclosure. However, terms maybe described differently in different contexts. Accordingly, thefollowing definitions should be considered as a supplement and shouldnot be considered to limit any other definitions of descriptionsprovided for such terms herein.

A bitstream is a sequence of bits including video data that iscompressed for transmission between an encoder and a decoder. An encoderis a device that is configured to employ encoding processes to compressvideo data into a bitstream. A decoder is a device that is configured toemploy decoding processes to reconstruct video data from a bitstream fordisplay. A picture is an array of luma samples and/or an array of chromasamples that create a frame or a field thereof. A picture that is beingencoded or decoded can be referred to as a current picture for clarityof discussion. A network abstraction layer (NAL) unit is a syntaxstructure containing data in the form of a Raw Byte Sequence Payload(RBSP), an indication of the type of data, and emulation preventionbytes, which are interspersed as desired. A video coding layer (VCL) NALunit is a NAL unit coded to contain video data, such as a coded slice ofa picture. A non-VCL NAL unit is a NAL unit that contains non-video datasuch as syntax and/or parameters that support decoding the video data,performance of conformance checking, or other operations. An access unit(AU) is a set of NAL units that are associated with each other accordingto a specified classification rule and pertain to one particular outputtime. A decoding unit (DU) is an AU or a sub-set of an AU and associatednon-VCL NAL units. For example, an AU includes VCL NAL units and anynon-VCL NAL units associated with the VCL NAL units in the AU. Further,the DU includes the set of VCL NAL units from the AU or a subsetthereof, as well as any non-VCL NAL units associated with the VCL NALunits in the DU. A layer is a set of VCL NAL units that share aspecified characteristic (e.g., a common resolution, frame rate, imagesize, etc.) and associated non-VCL NAL units. A decoding order is anorder in which syntax elements are processed by a decoding process. Avideo parameter set (VPS) is a data unit that contains parametersrelated to an entire video.

A temporal scalable bitstream is a bitstream coded in multiple layersproviding varying temporal resolution/frame rate (e.g., each layer iscoded to support a different frame rate). A sublayer is a temporalscalable layer of a temporal scalable bitstream including VCL NAL unitswith a particular temporal identifier value and associated non-VCL NALunits. For example, a temporal sublayer is a layer that contains videodata associated with a specified frame rate. A sublayer representationis a subset of the bitstream containing NAL units of a particularsublayer and the lower sublayers. Hence, one or more temporal sublayersmay be combined to achieve a sublayer representation that can be decodedto result in a video sequence with a specified frame rate. An outputlayer set (OLS) is a set of layers for which one or more layers arespecified as output layer(s). An output layer is a layer that isdesignated for output (e.g., to a display). An OLS index is an indexthat uniquely identifies a corresponding OLS. A zeroth (0-th) OLS is anOLS that contains only a lowest layer (layer with a lowest layeridentifier) and hence contains only an output layer. A temporalidentifier (ID) is a data element that indicates data corresponds totemporal location in a video sequence. A sub-bitstream extractionprocess is a process that removes NAL units from a bitstream that do notbelong to a target set as determined by a target OLS index and a targethighest temporal ID. The sub-bitstream extraction process results in anoutput sub-bitstream containing NAL units from the bitstream that arepart of the target set.

A HRD is a decoder model operating on an encoder that checks thevariability of bitstreams produced by an encoding process to verifyconformance with specified constraints. A bitstream conformance test isa test to determine whether an encoded bitstream complies with astandard, such as Versatile Video Coding (VVC). HRD parameters aresyntax elements that initialize and/or define operational conditions ofan HRD. HRD parameters can be contained in a HRD parameter syntaxstructure. A syntax structure is a data object configured to include aplurality of different parameters. A syntax element is a data objectthat contains one or more parameters of the same type. Hence, a syntaxstructure can contain a plurality of syntax elements. Sequence-level HRDparameters are HRD parameters that apply to an entire coded videosequence. A maximum HRD temporal ID (hrd_max_tid[i]) specifies theTemporal ID of the highest sublayer representation for which the HRDparameters are contained in an i-th set of OLS HRD parameters. A generalHRD parameters (general_hrd_parameters) syntax structure is a syntaxstructure that contains sequence level HRD parameters. An operationpoint (OP) is a temporal subset of an OLS that is identified by an OLSindex and a highest temporal ID. An OP under test (targetOp) is an OPthat is selected for conformance testing at a HRD. A target OLS is anOLS that is selected for extraction from a bitstream. A decoding unitHRD parameters present flag (decoding_unit_hrd_params_present_flag) is aflag that indicates whether corresponding HRD parameters operate at a DUlevel or an AU level. A coded picture buffer (CPB) is a first-infirst-out buffer in a HRD that contains coded pictures in decoding orderfor use during bitstream conformance verification. A decoded picturebuffer (DPB) is a buffer for holding decoded pictures for reference,output reordering, and/or output delay.

A supplemental enhancement information (SEI) message is a syntaxstructure with specified semantics that conveys information that is notneeded by the decoding process in order to determine the values of thesamples in decoded pictures. A scalable-nesting SEI message is a messagethat contains a plurality of SEI messages that correspond to one or moreOLSs or one or more layers. A non-scalable-nested SEI message is amessage that is not nested and hence contains a single SEI message. Abuffering period (BP) SEI message is a SEI message that contains HRDparameters for initializing an HRD to manage a CPB. A picture timing(PT) SEI message is a SEI message that contains HRD parameters formanaging delivery information for AUs at the CPB and/or the DPB. Adecoding unit information (DUI) SEI message is a SEI message thatcontains HRD parameters for managing delivery information for DUs at theCPB and/or the DPB.

A CPB removal delay is a period of time that a corresponding current AUcan remain in the CPB prior to removal and output to a DPB. An initialCPB removal delay is a default CPB removal delay for each picture, AU,and/or DU in a bitstream, OLS, and/or layer. A CPB removal offset is alocation in the CPB used to determine boundaries of a corresponding AUin the CPB. An initial CPB removal offset is a default CPB removaloffset associated with each picture, AU, and/or DU in a bitstream, OLS,and/or layer. A decoded picture buffer (DPB) output delay information isa period of time that a corresponding AU can remain in the DPB prior tooutput. A CPB removal delay information is information related toremoval of a corresponding DU from the CPB. A delivery schedulespecifies timing for delivery of video data to and/or from a memorylocation, such as a CPB and/or a DPB. A VPS layer ID (vps_layer_id) is asyntax element that indicates the layer ID of an ith layer indicated inthe VPS. A total number of output layer sets minus one(num_output_layer_sets_minus1) plus one is a syntax element thatspecifies the total number of OLSs specified by the VPS. A HRD codedpicture buffer count (hrd_cpb_cnt_minus1) is a syntax element thatspecifies the number of alternative CPB delivery schedules. A sublayerCPB parameters present flag (sublayer_cpb_params_present_flag) is asyntax element that specifies whether a set of OLS HRD parametersincludes HRD parameters for specified sublayer representations. Aschedule index (ScIdx) is an index that identifies a delivery schedule.A BP CPB count minus1 (bp_cpb_cnt_minus1) is a syntax element thatspecifies a number of initial CPB remove delay and offset pairs, andhence the number of delivery schedules that are available for a temporalsublayer. A NAL unit header layer identifier (nuh_layer_id) is a syntaxelement that specifies an identifier of a layer that includes a NALunit. A fixed picture rate general flag (fixed_pic_rate_general_flag)syntax element is a syntax element that specifies whether a temporaldistance between HRD output times of consecutive pictures in outputorder is constrained. A sublayer HRD parameters(sublayer_hrd_parameters) syntax structure is a syntax structure thatincludes HRD parameters for a corresponding sublayer. A general VCL HRDparameters present flag (general_vcl_hrd_params_present_flag) is a flagthat specifies whether VCL HRD parameters are present in a general HRDparameters syntax structure. A BP maximum sublayers minus one(bp_max_sublayers_minus1) syntax element is a syntax element thatspecifies the maximum number of temporal sublayers for which CPB removaldelay and CPB removal offset are indicated in the BP SEI message. A VPSmaximum sublayers minus one (vps_max_sublayers_minus1) syntax element isa syntax element that specifies the maximum number of temporal sublayersthat may be present in a layer specified by the VPS. A scalable nestingOLS flag is a flag that specifies whether scalable-nested SEI messagesapply to specific OLSs or specific layers. A scalable nesting number ofOLSs minus one (num_olss_minus1) is a syntax element that specifies thenumber of OLSs to which the scalable-nested SEI messages apply. Anesting OLS index (NestingOlsIdx) is a syntax element that specifies theOLS index of the OLS to which the scalable-nested SEI messages apply. Atarget OLS index (targetOlsIdx) is a variable that identifies the OLSindex of a target OLS to be decoded. A total number of OLSs minus one(TotalNumOlss−1) is a syntax element that specifies a total number ofOLSs specified in a VPS.

The following acronyms are used herein, Access Unit (AU), Coding TreeBlock (CTB), Coding Tree Unit (CTU), Coding Unit (CU), Coded Layer VideoSequence (CLVS), Coded Layer Video Sequence Start (CLVSS), Coded VideoSequence (CVS), Coded Video Sequence Start (CVSS), Joint Video ExpertsTeam (JVET), Hypothetical Reference Decoder (HRD), Motion ConstrainedTile Set (MCTS), Maximum Transfer Unit (MTU), Network Abstraction Layer(NAL), Output Layer Set (OLS), Picture Order Count (POC), Random AccessPoint (RAP), Raw Byte Sequence Payload (RBSP), Sequence Parameter Set(SPS), Video Parameter Set (VPS), Versatile Video Coding (VVC).

Many video compression techniques can be employed to reduce the size ofvideo files with minimal loss of data. For example, video compressiontechniques can include performing spatial (e.g., intra-picture)prediction and/or temporal (e.g., inter-picture) prediction to reduce orremove data redundancy in video sequences. For block-based video coding,a video slice (e.g., a video picture or a portion of a video picture)may be partitioned into video blocks, which may also be referred to astreeblocks, coding tree blocks (CTBs), coding tree units (CTUs), codingunits (CUs), and/or coding nodes. Video blocks in an intra-coded (I)slice of a picture are coded using spatial prediction with respect toreference samples in neighboring blocks in the same picture. Videoblocks in an inter-coded unidirectional prediction (P) or bidirectionalprediction (B) slice of a picture may be coded by employing spatialprediction with respect to reference samples in neighboring blocks inthe same picture or temporal prediction with respect to referencesamples in other reference pictures. Pictures may be referred to asframes and/or images, and reference pictures may be referred to asreference frames and/or reference images. Spatial or temporal predictionresults in a predictive block representing an image block. Residual datarepresents pixel differences between the original image block and thepredictive block. Accordingly, an inter-coded block is encoded accordingto a motion vector that points to a block of reference samples formingthe predictive block and the residual data indicating the differencebetween the coded block and the predictive block. An intra-coded blockis encoded according to an intra-coding mode and the residual data. Forfurther compression, the residual data may be transformed from the pixeldomain to a transform domain. These result in residual transformcoefficients, which may be quantized. The quantized transformcoefficients may initially be arranged in a two-dimensional array. Thequantized transform coefficients may be scanned in order to produce aone-dimensional vector of transform coefficients. Entropy coding may beapplied to achieve even more compression. Such video compressiontechniques are discussed in greater detail below.

To ensure an encoded video can be accurately decoded, video is encodedand decoded according to corresponding video coding standards. Videocoding standards include International Telecommunication Union (ITU)Standardization Sector (ITU-T) H.261, International Organization forStandardization/International Electrotechnical Commission (ISO/IEC)Motion Picture Experts Group (MPEG)-1 Part 2, ITU-T H.262 or ISO/IECMPEG-2 Part 2, ITU-T H.263, ISO/IEC MPEG-4 Part 2, Advanced Video Coding(AVC), also known as ITU-T H.264 or ISO/IEC MPEG-4 Part 10, and HighEfficiency Video Coding (HEVC), also known as ITU-T H.265 or MPEG-H Part2. AVC includes extensions such as Scalable Video Coding (SVC),Multiview Video Coding (MVC) and Multiview Video Coding plus Depth(MVC+D), and three dimensional (3D) AVC (3D-AVC). HEVC includesextensions such as Scalable HEVC (SHVC), Multiview HEVC (MV-HEVC), and3D HEVC (3D-HEVC). The joint video experts team (JVET) of ITU-T andISO/IEC has begun developing a video coding standard referred to asVersatile Video Coding (VVC). VVC is included in a Working Draft (WD),which includes JVET-O2001-v14.

Video coding systems employ various conformance tests to ensure abitstream is decodable by a decoder. For example, a conformance checkmay include testing the entire bitstream for conformance, then testingeach layer of the bitstream for conformance, and finally checkingpotential decodable outputs for conformance. In order to implementconformance checks, corresponding parameters are included in thebitstream. A hypothetical reference decoder (HRD) can read theparameters and perform the tests. A video may include many layers andmany different output layer sets (OLSs). Upon request, the encodertransmits one or more layers of a selected OLS. For example, the encodermay transmit the best layer(s) from an OLS that can be supported by thecurrent network bandwidth. A first problem with this approach is that asignificant number of layers are tested, but not actually transmitted tothe decoder. However, the parameters to support such testing may stillbe included in the bitstream, which needlessly increases the bitstreamsize.

In a first example, disclosed herein is a mechanism to apply bitstreamconformance tests to each OLS only. In this way, the entire bitstream,each layer, and the decodable outputs are collectively tested when thecorresponding OLS is tested. Therefore, the number of conformance testsis reduced, which reduces processor and memory resource usage at theencoder. Further, reducing the number of conformance tests may reducethe number of associated parameters included in the bitstream. Thisdecreases bitstream size, and hence reduces processor, memory, and/ornetwork resource utilization at both the encoder and the decoder.

A second problem is that the HRD parameter signaling process used forHRD conformance testing in some video coding systems can becomecomplicated in the multi-layer context. For example, a set of HRDparameters can be signaled for each layer in each OLS. Such HRDparameters can be signaled in different locations in the bitstreamdepending on the intended scope of the parameters. This results in ascheme that becomes more complicated as more layers and/or OLSs areadded. Further, the HRD parameters for different layers and/or OLSs maycontain redundant information.

In a second example, disclosed herein is a mechanism for signaling aglobal set of HRD parameters for OLSs and corresponding layers. Forexample, all sequence-level HRD parameters that apply to all OLSs andall layers contained in the OLSs are signaled in a video parameter set(VPS). The VPS is signaled once in the bitstream, and therefore thesequence level HRD parameters are signaled once. Further, thesequence-level HRD parameters may be constrained to be the same for allOLSs. In this way, redundant signaling is decreased, which increasescoding efficiency. Also, this approach simplifies the HRD process. As aresult, processor, memory, and/or network signaling resource usage isreduced at both the encoder and the decoder.

A third problem may occur when video coding systems perform conformancechecks on bitstreams. Video may be coded into multiple layers and/orsublayers, which can then be organized into OLSs. Each layer and/orsublayer of each OLS is checked for conformance according to deliveryschedules. Each delivery schedule is associated with a different codedpicture buffer (CPB) size and CPB delay to account for differenttransmission bandwidths and system capabilities. Some video codingsystems allow each sublayer to define any number of delivery schedules.This may result in a large amount of signaling to support conformancechecks, which results in reduced coding efficiency for the bitstream.

In a third example, disclosed herein are mechanisms for increasingcoding efficiency for video including multiple layers. Specifically, alllayers and/or sub-layers are constrained to include the same number ofCPB delivery schedules. For example, the encoder can determine themaximum number of CPB delivery schedules used for any one layer and setthe number of CPB delivery schedules for all layers to the maximumnumber. The number of delivery schedules may then be signaled once, forexample as part of the HRD parameters in a VPS. This avoids a need tosignal a number of schedules for each layer/sublayer. In some examples,all layers/sublayers in an OLS can also share the same delivery scheduleindex. These changes reduce the amount of data used to signal datarelated to conformance checking. This decreases bitstream size, andhence reduces processor, memory, and/or network resource utilization atboth the encoder and the decoder.

A fourth problem may occur when video is coded into multiple layersand/or sublayers, which are then organized into OLSs. The OLSs mayinclude a zeroth (0-th) OLS that includes only an output layer.Supplemental enhancement information (SEI) messages may be included inthe bitstream to inform a HRD of layer/OLS specific parameters used totest the layers of the bitstream for conformance to standards.Specifically, scalable nesting SEI messages are employed when OLSs areincluded in the bitstream. A scalable nesting SEI message containsgroups of nested SEI messages that apply to one or more OLS and/or oneor more layers of an OLS. The nested SEI messages may each contain anindicator to indicate an association with a corresponding OLS and/orlayer. A nested SEI message is configured for use with multiple layersand may contain extraneous information when applied to a 0-th OLScontaining a single layer.

In a fourth example, disclosed herein is a mechanism for increasingcoding efficiency for video including a 0-th OLS. A non-scalable-nestedSEI message is employed for the 0-th OLS. The non-scalable-nested SEImessage is constrained to apply only to the 0-th OLS and hence only tothe output layer contained in the 0-th OLS. In this way, the extraneousinformation, such as nesting relationships, layer indications, etc., canbe omitted from the SEI message. The non-scalable-nested SEI message maybe used as a buffering period (BP) SEI message, a picture timing (PT)SEI message, a decoding unit (DU) SEI message, or combinations thereof.These changes reduce the amount of data used to signal conformancechecking related information for the 0-th OLS. This decreases bitstreamsize, and hence reduces processor, memory, and/or network resourceutilization at both the encoder and the decoder.

A fifth problem may also occur when video is separated into multiplelayers and/or sublayers. An encoder can encode these layers into abitstream. Further, the encoder may employ a HRD to perform conformancetests in order to check the bitstream for conformance with standards.The encoder may be configured to include layer-specific HRD parametersinto the bitstream to support such conformance tests. The layer-specificHRD parameters may be encoded for each layer in some video codingsystems. In some cases, the layer-specific HRD parameters are the samefor each layer, which results in redundant information thatunnecessarily increases the size of the video encoding.

In a fifth example, disclosed herein are mechanisms to reduce HRDparameter redundancy for videos that employ multiple layers. The encodercan encode HRD parameters for a highest layer. The encoder can alsoencode a sublayer CPB parameters present flag(sublayer_cpb_params_present_flag). The sublayer_cpb_params_present_flagcan be set to zero to indicate that all lower layers should use the sameHRD parameters as the highest layer. In this context, a highest layerhas a largest layer identifier (ID) and a lower layer is any layer thathas a layer ID that is smaller than the layer ID of the highest layer.In this way, the HRD parameters for the lower layers can be omitted fromthe bitstream. This decreases bitstream size, and hence reducesprocessor, memory, and/or network resource utilization at both theencoder and the decoder.

A sixth problem relates to the usage of sequence parameter sets (SPSs)to contain syntax elements related to each video sequence in a video.Video coding systems may code video in layers and/or sublayers. Videosequences may operate differently at different layers and/or sublayers.Hence, different layers may refer to different SPSs. A BP SEI messagemay indicate the layers/sublayers to be checked for conformance tostandards. Some video coding systems may indicate that the BP SEImessage applies to the layers/sublayers indicated in the SPS. This maycause problems when different layers have referenced different SPSs assuch SPSs may include contradictory information, which results inunexpected errors.

In a sixth example, disclosed herein are mechanisms to address errorsrelating to conformance checking when multiple layers are employed in avideo sequence. Specifically, the BP SEI message is modified to indicatethat any number of layers/sublayers described in a VPS may be checkedfor conformance. For example, the BP SEI message may contain a BPmaximum sublayers minus one (bp_max_sublayers_minus1) syntax elementthat indicates the number of layers/sublayers that are associated withthe data in the BP SEI message. Meanwhile, a VPS maximum sublayers minusone (vps_max_sublayers_minus1) syntax element in the VPS indicates thenumber of sublayers in the entire video. The bp_max_sublayers_minus1syntax element may be set to any value from zero to the value of thevps_max_sublayers_minus1 syntax element. In this way, any number oflayers/sublayers in the video can be checked for conformance whileavoiding layer based sequence issues related to SPS inconstancies.Accordingly, the present disclosure avoids layer based coding errors,and hence increases the functionality of an encoder and/or a decoder.Further, the present example supports layer based coding, which mayincrease coding efficiency. As such, the present example supportsreduced processor, memory, and/or network resource usage at an encoderand/or a decoder.

A seventh problem relates to layers that are included in OLSs. Each OLScontains at least one output layer that is configured to be displayed ata decoder. The HRD at the encoder can check each OLS for conformancewith standards. A conforming OLS can always be decoded and displayed ata conforming decoder. The HRD process may be managed in part by SEImessages. For example, a scalable nesting SEI message may containscalable nested SEI messages. Each scalable nested SEI message maycontain data that is relevant to a corresponding layer. When performinga conformance check, the HRD may perform a bitstream extraction processon a target OLS. Data that is not relevant to the layers in the OLS aregenerally removed prior to conformance testing so that each OLS can bechecked separately (e.g., prior to transmission). Some video codingsystems do not remove scalable nesting SEI messages during thesub-bitstream extraction process because such messages relate tomultiple layers. This may result in scalable nesting SEI messages thatremain in the bitstream after sub-bitstream extraction even when thescalable nesting SEI messages are not relevant to any layer in thetarget OLS (the OLS being extracted). This may increase the size of thefinal bitstream without providing any additional functionality.

In a seventh example, disclosed herein are mechanisms to reduce the sizeof multi-layer bitstreams. During sub-bitstream extraction, the scalablenesting SEI messages can be considered for removal from the bitstream.When a scalable nesting SEI message relates to one or more OLSs, thescalable nested SEI messages in the scalable nesting SEI message arechecked. When the scalable nested SEI messages do not relate to anylayer in the target OLS, then the entire scalable nesting SEI messagecan be removed from the bitstream. This results in reducing the size ofthe bitstream to be sent to the decoder. Accordingly, the presentexamples increase coding efficiency and reduce processor, memory, and/ornetwork resource usage at both the encoder and decoder.

FIG. 1 is a flowchart of an example operating method 100 of coding avideo signal. Specifically, a video signal is encoded at an encoder. Theencoding process compresses the video signal by employing variousmechanisms to reduce the video file size. A smaller file size allows thecompressed video file to be transmitted toward a user, while reducingassociated bandwidth overhead. The decoder then decodes the compressedvideo file to reconstruct the original video signal for display to anend user. The decoding process generally mirrors the encoding process toallow the decoder to consistently reconstruct the video signal.

At step 101, the video signal is input into the encoder. For example,the video signal may be an uncompressed video file stored in memory. Asanother example, the video file may be captured by a video capturedevice, such as a video camera, and encoded to support live streaming ofthe video. The video file may include both an audio component and avideo component. The video component contains a series of image framesthat, when viewed in a sequence, gives the visual impression of motion.The frames contain pixels that are expressed in terms of light, referredto herein as luma components (or luma samples), and color, which isreferred to as chroma components (or color samples). In some examples,the frames may also contain depth values to support three dimensionalviewing.

At step 103, the video is partitioned into blocks. Partitioning includessubdividing the pixels in each frame into square and/or rectangularblocks for compression. For example, in High Efficiency Video Coding(HEVC) (also known as H.265 and MPEG-H Part 2) the frame can first bedivided into coding tree units (CTUs), which are blocks of a predefinedsize (e.g., sixty-four pixels by sixty-four pixels). The CTUs containboth luma and chroma samples. Coding trees may be employed to divide theCTUs into blocks and then recursively subdivide the blocks untilconfigurations are achieved that support further encoding. For example,luma components of a frame may be subdivided until the individual blockscontain relatively homogenous lighting values. Further, chromacomponents of a frame may be subdivided until the individual blockscontain relatively homogenous color values. Accordingly, partitioningmechanisms vary depending on the content of the video frames.

At step 105, various compression mechanisms are employed to compress theimage blocks partitioned at step 103. For example, inter-predictionand/or intra-prediction may be employed. Inter-prediction is designed totake advantage of the fact that objects in a common scene tend to appearin successive frames. Accordingly, a block depicting an object in areference frame need not be repeatedly described in adjacent frames.Specifically, an object, such as a table, may remain in a constantposition over multiple frames. Hence the table is described once andadjacent frames can refer back to the reference frame. Pattern matchingmechanisms may be employed to match objects over multiple frames.Further, moving objects may be represented across multiple frames, forexample due to object movement or camera movement. As a particularexample, a video may show an automobile that moves across the screenover multiple frames. Motion vectors can be employed to describe suchmovement. A motion vector is a two-dimensional vector that provides anoffset from the coordinates of an object in a frame to the coordinatesof the object in a reference frame. As such, inter-prediction can encodean image block in a current frame as a set of motion vectors indicatingan offset from a corresponding block in a reference frame.

Intra-prediction encodes blocks in a common frame. Intra-predictiontakes advantage of the fact that luma and chroma components tend tocluster in a frame. For example, a patch of green in a portion of a treetends to be positioned adjacent to similar patches of green.Intra-prediction employs multiple directional prediction modes (e.g.,thirty-three in HEVC), a planar mode, and a direct current (DC) mode.The directional modes indicate that a current block is similar/the sameas samples of a neighbor block in a corresponding direction. Planar modeindicates that a series of blocks along a row/column (e.g., a plane) canbe interpolated based on neighbor blocks at the edges of the row. Planarmode, in effect, indicates a smooth transition of light/color across arow/column by employing a relatively constant slope in changing values.DC mode is employed for boundary smoothing and indicates that a block issimilar/the same as an average value associated with samples of all theneighbor blocks associated with the angular directions of thedirectional prediction modes. Accordingly, intra-prediction blocks canrepresent image blocks as various relational prediction mode valuesinstead of the actual values. Further, inter-prediction blocks canrepresent image blocks as motion vector values instead of the actualvalues. In either case, the prediction blocks may not exactly representthe image blocks in some cases. Any differences are stored in residualblocks. Transforms may be applied to the residual blocks to furthercompress the file.

At step 107, various filtering techniques may be applied. In HEVC, thefilters are applied according to an in-loop filtering scheme. The blockbased prediction discussed above may result in the creation of blockyimages at the decoder. Further, the block based prediction scheme mayencode a block and then reconstruct the encoded block for later use as areference block. The in-loop filtering scheme iteratively applies noisesuppression filters, de-blocking filters, adaptive loop filters, andsample adaptive offset (SAO) filters to the blocks/frames. These filtersmitigate such blocking artifacts so that the encoded file can beaccurately reconstructed. Further, these filters mitigate artifacts inthe reconstructed reference blocks so that artifacts are less likely tocreate additional artifacts in subsequent blocks that are encoded basedon the reconstructed reference blocks.

Once the video signal has been partitioned, compressed, and filtered,the resulting data is encoded in a bitstream at step 109. The bitstreamincludes the data discussed above as well as any signaling data desiredto support proper video signal reconstruction at the decoder. Forexample, such data may include partition data, prediction data, residualblocks, and various flags providing coding instructions to the decoder.The bitstream may be stored in memory for transmission toward a decoderupon request. The bitstream may also be broadcast and/or multicasttoward a plurality of decoders. The creation of the bitstream is aniterative process. Accordingly, steps 101, 103, 105, 107, and 109 mayoccur continuously and/or simultaneously over many frames and blocks.The order shown in FIG. 1 is presented for clarity and ease ofdiscussion, and is not intended to limit the video coding process to aparticular order.

The decoder receives the bitstream and begins the decoding process atstep 111. Specifically, the decoder employs an entropy decoding schemeto convert the bitstream into corresponding syntax and video data. Thedecoder employs the syntax data from the bitstream to determine thepartitions for the frames at step 111. The partitioning should match theresults of block partitioning at step 103. Entropy encoding/decoding asemployed in step 111 is now described. The encoder makes many choicesduring the compression process, such as selecting block partitioningschemes from several possible choices based on the spatial positioningof values in the input image(s). Signaling the exact choices may employa large number of bins. As used herein, a bin is a binary value that istreated as a variable (e.g., a bit value that may vary depending oncontext). Entropy coding allows the encoder to discard any options thatare clearly not viable for a particular case, leaving a set of allowableoptions. Each allowable option is then assigned a code word. The lengthof the code words is based on the number of allowable options (e.g., onebin for two options, two bins for three to four options, etc.) Theencoder then encodes the code word for the selected option. This schemereduces the size of the code words as the code words are as big asdesired to uniquely indicate a selection from a small sub-set ofallowable options as opposed to uniquely indicating the selection from apotentially large set of all possible options. The decoder then decodesthe selection by determining the set of allowable options in a similarmanner to the encoder. By determining the set of allowable options, thedecoder can read the code word and determine the selection made by theencoder.

At step 113, the decoder performs block decoding. Specifically, thedecoder employs reverse transforms to generate residual blocks. Then thedecoder employs the residual blocks and corresponding prediction blocksto reconstruct the image blocks according to the partitioning. Theprediction blocks may include both intra-prediction blocks andinter-prediction blocks as generated at the encoder at step 105. Thereconstructed image blocks are then positioned into frames of areconstructed video signal according to the partitioning data determinedat step 111. Syntax for step 113 may also be signaled in the bitstreamvia entropy coding as discussed above.

At step 115, filtering is performed on the frames of the reconstructedvideo signal in a manner similar to step 107 at the encoder. Forexample, noise suppression filters, de-blocking filters, adaptive loopfilters, and SAO filters may be applied to the frames to remove blockingartifacts. Once the frames are filtered, the video signal can be outputto a display at step 117 for viewing by an end user.

FIG. 2 is a schematic diagram of an example coding and decoding (codec)system 200 for video coding. Specifically, codec system 200 providesfunctionality to support the implementation of operating method 100.Codec system 200 is generalized to depict components employed in both anencoder and a decoder. Codec system 200 receives and partitions a videosignal as discussed with respect to steps 101 and 103 in operatingmethod 100, which results in a partitioned video signal 201. Codecsystem 200 then compresses the partitioned video signal 201 into a codedbitstream when acting as an encoder as discussed with respect to steps105, 107, and 109 in method 100. When acting as a decoder, codec system200 generates an output video signal from the bitstream as discussedwith respect to steps 111, 113, 115, and 117 in operating method 100.The codec system 200 includes a general coder control component 211, atransform scaling and quantization component 213, an intra-pictureestimation component 215, an intra-picture prediction component 217, amotion compensation component 219, a motion estimation component 221, ascaling and inverse transform component 229, a filter control analysiscomponent 227, an in-loop filters component 225, a decoded picturebuffer component 223, and a header formatting and context adaptivebinary arithmetic coding (CABAC) component 231. Such components arecoupled as shown. In FIG. 2, black lines indicate movement of data to beencoded/decoded while dashed lines indicate movement of control datathat controls the operation of other components. The components of codecsystem 200 may all be present in the encoder. The decoder may include asubset of the components of codec system 200. For example, the decodermay include the intra-picture prediction component 217, the motioncompensation component 219, the scaling and inverse transform component229, the in-loop filters component 225, and the decoded picture buffercomponent 223. These components are now described.

The partitioned video signal 201 is a captured video sequence that hasbeen partitioned into blocks of pixels by a coding tree. A coding treeemploys various split modes to subdivide a block of pixels into smallerblocks of pixels. These blocks can then be further subdivided intosmaller blocks. The blocks may be referred to as nodes on the codingtree. Larger parent nodes are split into smaller child nodes. The numberof times a node is subdivided is referred to as the depth of thenode/coding tree. The divided blocks can be included in coding units(CUs) in some cases. For example, a CU can be a sub-portion of a CTUthat contains a luma block, red difference chroma (Cr) block(s), and ablue difference chroma (Cb) block(s) along with corresponding syntaxinstructions for the CU. The split modes may include a binary tree (BT),triple tree (TT), and a quad tree (QT) employed to partition a node intotwo, three, or four child nodes, respectively, of varying shapesdepending on the split modes employed. The partitioned video signal 201is forwarded to the general coder control component 211, the transformscaling and quantization component 213, the intra-picture estimationcomponent 215, the filter control analysis component 227, and the motionestimation component 221 for compression.

The general coder control component 211 is configured to make decisionsrelated to coding of the images of the video sequence into the bitstreamaccording to application constraints. For example, the general codercontrol component 211 manages optimization of bitrate/bitstream sizeversus reconstruction quality. Such decisions may be made based onstorage space/bandwidth availability and image resolution requests. Thegeneral coder control component 211 also manages buffer utilization inlight of transmission speed to mitigate buffer underrun and overrunissues. To manage these issues, the general coder control component 211manages partitioning, prediction, and filtering by the other components.For example, the general coder control component 211 may dynamicallyincrease compression complexity to increase resolution and increasebandwidth usage or decrease compression complexity to decreaseresolution and bandwidth usage. Hence, the general coder controlcomponent 211 controls the other components of codec system 200 tobalance video signal reconstruction quality with bit rate concerns. Thegeneral coder control component 211 creates control data, which controlsthe operation of the other components. The control data is alsoforwarded to the header formatting and CABAC component 231 to be encodedin the bitstream to signal parameters for decoding at the decoder.

The partitioned video signal 201 is also sent to the motion estimationcomponent 221 and the motion compensation component 219 forinter-prediction. A frame or slice of the partitioned video signal 201may be divided into multiple video blocks. Motion estimation component221 and the motion compensation component 219 perform inter-predictivecoding of the received video block relative to one or more blocks in oneor more reference frames to provide temporal prediction. Codec system200 may perform multiple coding passes, e.g., to select an appropriatecoding mode for each block of video data.

Motion estimation component 221 and motion compensation component 219may be highly integrated, but are illustrated separately for conceptualpurposes. Motion estimation, performed by motion estimation component221, is the process of generating motion vectors, which estimate motionfor video blocks. A motion vector, for example, may indicate thedisplacement of a coded object relative to a predictive block. Apredictive block is a block that is found to closely match the block tobe coded, in terms of pixel difference. A predictive block may also bereferred to as a reference block. Such pixel difference may bedetermined by sum of absolute difference (SAD), sum of square difference(SSD), or other difference metrics. HEVC employs several coded objectsincluding a CTU, coding tree blocks (CTBs), and CUs. For example, a CTUcan be divided into CTBs, which can then be divided into CBs forinclusion in CUs. A CU can be encoded as a prediction unit (PU)containing prediction data and/or a transform unit (TU) containingtransformed residual data for the CU. The motion estimation component221 generates motion vectors, PUs, and TUs by using a rate-distortionanalysis as part of a rate distortion optimization process. For example,the motion estimation component 221 may determine multiple referenceblocks, multiple motion vectors, etc. for a current block/frame, and mayselect the reference blocks, motion vectors, etc. having the bestrate-distortion characteristics. The best rate-distortioncharacteristics balance both quality of video reconstruction (e.g.,amount of data loss by compression) with coding efficiency (e.g., sizeof the final encoding).

In some examples, codec system 200 may calculate values for sub-integerpixel positions of reference pictures stored in decoded picture buffercomponent 223. For example, video codec system 200 may interpolatevalues of one-quarter pixel positions, one-eighth pixel positions, orother fractional pixel positions of the reference picture. Therefore,motion estimation component 221 may perform a motion search relative tothe full pixel positions and fractional pixel positions and output amotion vector with fractional pixel precision. The motion estimationcomponent 221 calculates a motion vector for a PU of a video block in aninter-coded slice by comparing the position of the PU to the position ofa predictive block of a reference picture. Motion estimation component221 outputs the calculated motion vector as motion data to headerformatting and CABAC component 231 for encoding and motion to the motioncompensation component 219.

Motion compensation, performed by motion compensation component 219, mayinvolve fetching or generating the predictive block based on the motionvector determined by motion estimation component 221. Again, motionestimation component 221 and motion compensation component 219 may befunctionally integrated, in some examples. Upon receiving the motionvector for the PU of the current video block, motion compensationcomponent 219 may locate the predictive block to which the motion vectorpoints. A residual video block is then formed by subtracting pixelvalues of the predictive block from the pixel values of the currentvideo block being coded, forming pixel difference values. In general,motion estimation component 221 performs motion estimation relative toluma components, and motion compensation component 219 uses motionvectors calculated based on the luma components for both chromacomponents and luma components. The predictive block and residual blockare forwarded to transform scaling and quantization component 213.

The partitioned video signal 201 is also sent to intra-pictureestimation component 215 and intra-picture prediction component 217. Aswith motion estimation component 221 and motion compensation component219, intra-picture estimation component 215 and intra-picture predictioncomponent 217 may be highly integrated, but are illustrated separatelyfor conceptual purposes. The intra-picture estimation component 215 andintra-picture prediction component 217 intra-predict a current blockrelative to blocks in a current frame, as an alternative to theinter-prediction performed by motion estimation component 221 and motioncompensation component 219 between frames, as described above. Inparticular, the intra-picture estimation component 215 determines anintra-prediction mode to use to encode a current block. In someexamples, intra-picture estimation component 215 selects an appropriateintra-prediction mode to encode a current block from multiple testedintra-prediction modes. The selected intra-prediction modes are thenforwarded to the header formatting and CABAC component 231 for encoding.

For example, the intra-picture estimation component 215 calculatesrate-distortion values using a rate-distortion analysis for the varioustested intra-prediction modes, and selects the intra-prediction modehaving the best rate-distortion characteristics among the tested modes.Rate-distortion analysis generally determines an amount of distortion(or error) between an encoded block and an original unencoded block thatwas encoded to produce the encoded block, as well as a bitrate (e.g., anumber of bits) used to produce the encoded block. The intra-pictureestimation component 215 calculates ratios from the distortions andrates for the various encoded blocks to determine which intra-predictionmode exhibits the best rate-distortion value for the block. In addition,intra-picture estimation component 215 may be configured to code depthblocks of a depth map using a depth modeling mode (DMM) based onrate-distortion optimization (RDO).

The intra-picture prediction component 217 may generate a residual blockfrom the predictive block based on the selected intra-prediction modesdetermined by intra-picture estimation component 215 when implemented onan encoder or read the residual block from the bitstream whenimplemented on a decoder. The residual block includes the difference invalues between the predictive block and the original block, representedas a matrix. The residual block is then forwarded to the transformscaling and quantization component 213. The intra-picture estimationcomponent 215 and the intra-picture prediction component 217 may operateon both luma and chroma components.

The transform scaling and quantization component 213 is configured tofurther compress the residual block. The transform scaling andquantization component 213 applies a transform, such as a discretecosine transform (DCT), a discrete sine transform (DST), or aconceptually similar transform, to the residual block, producing a videoblock comprising residual transform coefficient values. Wavelettransforms, integer transforms, sub-band transforms or other types oftransforms could also be used. The transform may convert the residualinformation from a pixel value domain to a transform domain, such as afrequency domain. The transform scaling and quantization component 213is also configured to scale the transformed residual information, forexample based on frequency. Such scaling involves applying a scalefactor to the residual information so that different frequencyinformation is quantized at different granularities, which may affectfinal visual quality of the reconstructed video. The transform scalingand quantization component 213 is also configured to quantize thetransform coefficients to further reduce bit rate. The quantizationprocess may reduce the bit depth associated with some or all of thecoefficients. The degree of quantization may be modified by adjusting aquantization parameter. In some examples, the transform scaling andquantization component 213 may then perform a scan of the matrixincluding the quantized transform coefficients. The quantized transformcoefficients are forwarded to the header formatting and CABAC component231 to be encoded in the bitstream.

The scaling and inverse transform component 229 applies a reverseoperation of the transform scaling and quantization component 213 tosupport motion estimation. The scaling and inverse transform component229 applies inverse scaling, transformation, and/or quantization toreconstruct the residual block in the pixel domain, e.g., for later useas a reference block which may become a predictive block for anothercurrent block. The motion estimation component 221 and/or motioncompensation component 219 may calculate a reference block by adding theresidual block back to a corresponding predictive block for use inmotion estimation of a later block/frame. Filters are applied to thereconstructed reference blocks to mitigate artifacts created duringscaling, quantization, and transform. Such artifacts could otherwisecause inaccurate prediction (and create additional artifacts) whensubsequent blocks are predicted.

The filter control analysis component 227 and the in-loop filterscomponent 225 apply the filters to the residual blocks and/or toreconstructed image blocks. For example, the transformed residual blockfrom the scaling and inverse transform component 229 may be combinedwith a corresponding prediction block from intra-picture predictioncomponent 217 and/or motion compensation component 219 to reconstructthe original image block. The filters may then be applied to thereconstructed image block. In some examples, the filters may instead beapplied to the residual blocks. As with other components in FIG. 2, thefilter control analysis component 227 and the in-loop filters component225 are highly integrated and may be implemented together, but aredepicted separately for conceptual purposes. Filters applied to thereconstructed reference blocks are applied to particular spatial regionsand include multiple parameters to adjust how such filters are applied.The filter control analysis component 227 analyzes the reconstructedreference blocks to determine where such filters should be applied andsets corresponding parameters. Such data is forwarded to the headerformatting and CABAC component 231 as filter control data for encoding.The in-loop filters component 225 applies such filters based on thefilter control data. The filters may include a deblocking filter, anoise suppression filter, a SAO filter, and an adaptive loop filter.Such filters may be applied in the spatial/pixel domain (e.g., on areconstructed pixel block) or in the frequency domain, depending on theexample.

When operating as an encoder, the filtered reconstructed image block,residual block, and/or prediction block are stored in the decodedpicture buffer component 223 for later use in motion estimation asdiscussed above. When operating as a decoder, the decoded picture buffercomponent 223 stores and forwards the reconstructed and filtered blockstoward a display as part of an output video signal. The decoded picturebuffer component 223 may be any memory device capable of storingprediction blocks, residual blocks, and/or reconstructed image blocks.

The header formatting and CABAC component 231 receives the data from thevarious components of codec system 200 and encodes such data into acoded bitstream for transmission toward a decoder. Specifically, theheader formatting and CABAC component 231 generates various headers toencode control data, such as general control data and filter controldata. Further, prediction data, including intra-prediction and motiondata, as well as residual data in the form of quantized transformcoefficient data are all encoded in the bitstream. The final bitstreamincludes all information desired by the decoder to reconstruct theoriginal partitioned video signal 201. Such information may also includeintra-prediction mode index tables (also referred to as codeword mappingtables), definitions of encoding contexts for various blocks,indications of most probable intra-prediction modes, an indication ofpartition information, etc. Such data may be encoded by employingentropy coding. For example, the information may be encoded by employingcontext adaptive variable length coding (CAVLC), CABAC, syntax-basedcontext-adaptive binary arithmetic coding (SBAC), probability intervalpartitioning entropy (PIPE) coding, or another entropy coding technique.Following the entropy coding, the coded bitstream may be transmitted toanother device (e.g., a video decoder) or archived for latertransmission or retrieval.

FIG. 3 is a block diagram illustrating an example video encoder 300.Video encoder 300 may be employed to implement the encoding functions ofcodec system 200 and/or implement steps 101, 103, 105, 107, and/or 109of operating method 100. Encoder 300 partitions an input video signal,resulting in a partitioned video signal 301, which is substantiallysimilar to the partitioned video signal 201. The partitioned videosignal 301 is then compressed and encoded into a bitstream by componentsof encoder 300.

Specifically, the partitioned video signal 301 is forwarded to anintra-picture prediction component 317 for intra-prediction. Theintra-picture prediction component 317 may be substantially similar tointra-picture estimation component 215 and intra-picture predictioncomponent 217. The partitioned video signal 301 is also forwarded to amotion compensation component 321 for inter-prediction based onreference blocks in a decoded picture buffer component 323. The motioncompensation component 321 may be substantially similar to motionestimation component 221 and motion compensation component 219. Theprediction blocks and residual blocks from the intra-picture predictioncomponent 317 and the motion compensation component 321 are forwarded toa transform and quantization component 313 for transform andquantization of the residual blocks. The transform and quantizationcomponent 313 may be substantially similar to the transform scaling andquantization component 213. The transformed and quantized residualblocks and the corresponding prediction blocks (along with associatedcontrol data) are forwarded to an entropy coding component 331 forcoding into a bitstream. The entropy coding component 331 may besubstantially similar to the header formatting and CABAC component 231.

The transformed and quantized residual blocks and/or the correspondingprediction blocks are also forwarded from the transform and quantizationcomponent 313 to an inverse transform and quantization component 329 forreconstruction into reference blocks for use by the motion compensationcomponent 321. The inverse transform and quantization component 329 maybe substantially similar to the scaling and inverse transform component229. In-loop filters in an in-loop filters component 325 are alsoapplied to the residual blocks and/or reconstructed reference blocks,depending on the example. The in-loop filters component 325 may besubstantially similar to the filter control analysis component 227 andthe in-loop filters component 225. The in-loop filters component 325 mayinclude multiple filters as discussed with respect to in-loop filterscomponent 225. The filtered blocks are then stored in a decoded picturebuffer component 323 for use as reference blocks by the motioncompensation component 321. The decoded picture buffer component 323 maybe substantially similar to the decoded picture buffer component 223.

FIG. 4 is a block diagram illustrating an example video decoder 400.Video decoder 400 may be employed to implement the decoding functions ofcodec system 200 and/or implement steps 111, 113, 115, and/or 117 ofoperating method 100. Decoder 400 receives a bitstream, for example froman encoder 300, and generates a reconstructed output video signal basedon the bitstream for display to an end user.

The bitstream is received by an entropy decoding component 433. Theentropy decoding component 433 is configured to implement an entropydecoding scheme, such as CAVLC, CABAC, SBAC, PIPE coding, or otherentropy coding techniques. For example, the entropy decoding component433 may employ header information to provide a context to interpretadditional data encoded as codewords in the bitstream. The decodedinformation includes any desired information to decode the video signal,such as general control data, filter control data, partitioninformation, motion data, prediction data, and quantized transformcoefficients from residual blocks. The quantized transform coefficientsare forwarded to an inverse transform and quantization component 429 forreconstruction into residual blocks. The inverse transform andquantization component 429 may be similar to inverse transform andquantization component 329.

The reconstructed residual blocks and/or prediction blocks are forwardedto intra-picture prediction component 417 for reconstruction into imageblocks based on intra-prediction operations. The intra-pictureprediction component 417 may be similar to intra-picture estimationcomponent 215 and an intra-picture prediction component 217.Specifically, the intra-picture prediction component 417 employsprediction modes to locate a reference block in the frame and applies aresidual block to the result to reconstruct intra-predicted imageblocks. The reconstructed intra-predicted image blocks and/or theresidual blocks and corresponding inter-prediction data are forwarded toa decoded picture buffer component 423 via an in-loop filters component425, which may be substantially similar to decoded picture buffercomponent 223 and in-loop filters component 225, respectively. Thein-loop filters component 425 filters the reconstructed image blocks,residual blocks and/or prediction blocks, and such information is storedin the decoded picture buffer component 423. Reconstructed image blocksfrom decoded picture buffer component 423 are forwarded to a motioncompensation component 421 for inter-prediction. The motion compensationcomponent 421 may be substantially similar to motion estimationcomponent 221 and/or motion compensation component 219. Specifically,the motion compensation component 421 employs motion vectors from areference block to generate a prediction block and applies a residualblock to the result to reconstruct an image block. The resultingreconstructed blocks may also be forwarded via the in-loop filterscomponent 425 to the decoded picture buffer component 423. The decodedpicture buffer component 423 continues to store additional reconstructedimage blocks, which can be reconstructed into frames via the partitioninformation. Such frames may also be placed in a sequence. The sequenceis output toward a display as a reconstructed output video signal.

FIG. 5 is a schematic diagram illustrating an example HRD 500. A HRD 500may be employed in an encoder, such as codec system 200 and/or encoder300. The HRD 500 may check the bitstream created at step 109 of method100 before the bitstream is forwarded to a decoder, such as decoder 400.In some examples, the bitstream may be continuously forwarded throughthe HRD 500 as the bitstream is encoded. In the event that a portion ofthe bitstream fails to conform to associated constraints, the HRD 500can indicate such failure to an encoder to cause the encoder tore-encode the corresponding section of the bitstream with differentmechanisms.

The HRD 500 includes a hypothetical stream scheduler (HSS) 541. A HSS541 is a component configured to perform a hypothetical deliverymechanism. The hypothetical delivery mechanism is used for checking theconformance of a bitstream or a decoder with regards to the timing anddata flow of a bitstream 551 input into the HRD 500. For example, theHSS 541 may receive a bitstream 551 output from an encoder and managethe conformance testing process on the bitstream 551. In a particularexample, the HSS 541 can control the rate that coded pictures movethrough the HRD 500 and verify that the bitstream 551 does not containnon-conforming data.

The HSS 541 may forward the bitstream 551 to a CPB 543 at a predefinedrate. The HRD 500 may manage data in decoding units (DU) 553. A DU 553is an AU or a sub-set of an AU and associated non-video coding layer(VCL) network abstraction layer (NAL) units. Specifically, an AUcontains one or more pictures associated with an output time. Forexample, an AU may contain a single picture in a single layer bitstream,and may contain a picture for each layer in a multi-layer bitstream.Each picture of an AU may be divided into slices that are each includedin a corresponding VCL NAL unit. Hence, a DU 553 may contain one or morepictures, one or more slices of a picture, or combinations thereof.Also, parameters used to decode the AU, pictures, and/or slices can beincluded in non-VCL NAL units. As such, the DU 553 contains non-VCL NALunits that contain data needed to support decoding the VCL NAL units inthe DU 553. The CPB 543 is a first-in first-out buffer in the HRD 500.The CPB 543 contains DUs 553 including video data in decoding order. TheCPB 543 stores the video data for use during bitstream conformanceverification.

The CPB 543 forwards the DUs 553 to a decoding process component 545.The decoding process component 545 is a component that conforms to theVVC standard. For example, the decoding process component 545 mayemulate a decoder 400 employed by an end user. The decoding processcomponent 545 decodes the DUs 553 at a rate that can be achieved by anexample end user decoder. If the decoding process component 545 cannotdecode the DUs 553 fast enough to prevent an overflow of the CPB 543,then the bitstream 551 does not conform to the standard and should bere-encoded.

The decoding process component 545 decodes the DUs 553, which createsdecoded DUs 555. A decoded DU 555 contains a decoded picture. Thedecoded DUs 555 are forwarded to a DPB 547. The DPB 547 may besubstantially similar to a decoded picture buffer component 223, 323,and/or 423. To support inter-prediction, pictures that are marked foruse as reference pictures 556 that are obtained from the decoded DUs 555are returned to the decoding process component 545 to support furtherdecoding. The DPB 547 outputs the decoded video sequence as a series ofpictures 557. The pictures 557 are reconstructed pictures that generallymirror pictures encoded into the bitstream 551 by the encoder.

The pictures 557 are forwarded to an output cropping component 549. Theoutput cropping component 549 is configured to apply a conformancecropping window to the pictures 557. This results in output croppedpictures 559. An output cropped picture 559 is a completelyreconstructed picture. Accordingly, the output cropped picture 559mimics what an end user would see upon decoding the bitstream 551. Assuch, the encoder can review the output cropped pictures 559 to ensurethe encoding is satisfactory.

The HRD 500 is initialized based on HRD parameters in the bitstream 551.For example, the HRD 500 may read HRD parameters from a VPS, a SPS,and/or SEI messages. The HRD 500 may then perform conformance testingoperations on the bitstream 551 based on the information in such HRDparameters. As a specific example, the HRD 500 may determine one or moreCPB delivery schedules 561 from the HRD parameters. A delivery schedulespecifies timing for delivery of video data to and/or from a memorylocation, such as a CPB and/or a DPB. Hence, a CPB delivery schedule 561specifies timing for delivery of AUs, DUs 553, and/or pictures, to/fromthe CPB 543. For example, the CPB delivery schedule 561 may describe bitrates and buffer sizes for the CPB 543, where such bit rates and buffersizes corresponding to a particular class of decoder and/or networkcondition. Hence, the CPB delivery schedule 561 may indicate how longdata can remain in a CPB 543 prior to eviction. Failure to maintain theCPB delivery schedule 561 at the HRD 500 during a conformance test is anindication that a decoder that corresponds to the CPB delivery schedule561 would be unable to decode a corresponding bitstream. It should benoted that the HRD 500 may employ DPB delivery schedules for the DPB 547that are similar to the CPB delivery schedules 561.

Video may be coded into different layers and/or OLSs for use by decoderswith varying levels of hardware capabilities as well for varying networkconditions. The CPB delivery schedules 561 are selected to reflect theseissues. Accordingly, higher layer sub-bitstreams are designated foroptimal hardware and network conditions and hence higher layers mayreceive one or more CPB delivery schedules 561 that employ a largeamount of memory in the CPB 543 and short delays for transfers of theDUs 553 toward the DPB 547. Likewise, lower layer sub-bitstreams aredesignated for limited decoder hardware capabilities and/or poor networkconditions. Hence, lower layers may receive one or more CPB deliveryschedules 561 that employ a small amount of memory in the CPB 543 andlonger delays for transfers of the DUs 553 toward the DPB 547. The OLSs,layers, sublayers, or combinations thereof can then be tested accordingto the corresponding delivery schedule 561 to ensure that the resultingsub-bitstream can be correctly decoded under the conditions that areexpected for the sub-bitstream. The CPB delivery schedules 561 are eachassociated with a schedule index (ScIdx) 563. A ScIdx 563 is an indexthat identifies a delivery schedule. Accordingly, the HRD parameters inthe bitstream 551 can indicate the CPB delivery schedules 561 by ScIdx563 as well as include sufficient data to allow the HRD 500 to determinethe CPB delivery schedules 561 and correlate the CPB delivery schedules561 to the corresponding OLSs, layers, and/or sublayers.

FIG. 6 is a schematic diagram illustrating an example multi-layer videosequence 600 configured for inter-layer prediction 621. The multi-layervideo sequence 600 may be encoded by an encoder, such as codec system200 and/or encoder 300 and decoded by a decoder, such as codec system200 and/or decoder 400, for example according to method 100. Further,the multi-layer video sequence 600 can be checked for standardconformance by a HRD, such as HRD 500. The multi-layer video sequence600 is included to depict an example application for layers in a codedvideo sequence. A multi-layer video sequence 600 is any video sequencethat employs a plurality of layers, such as layer N 631 and layer N+1632.

In an example, the multi-layer video sequence 600 may employ inter-layerprediction 621. Inter-layer prediction 621 is applied between pictures611, 612, 613, and 614 and pictures 615, 616, 617, and 618 in differentlayers. In the example shown, pictures 611, 612, 613, and 614 are partof layer N+1 632 and pictures 615, 616, 617, and 618 are part of layer N631. A layer, such as layer N 631 and/or layer N+1 632, is a group ofpictures that are all associated with a similar value of acharacteristic, such as a similar size, quality, resolution, signal tonoise ratio, capability, etc. A layer may be defined formally as a setof VCL NAL units and associated non-VCL NAL units. A VCL NAL unit is aNAL unit coded to contain video data, such as a coded slice of apicture. A non-VCL NAL unit is a NAL unit that contains non-video datasuch as syntax and/or parameters that support decoding the video data,performance of conformance checking, or other operations.

In the example show, layer N+1 632 is associated with a larger imagesize than layer N 631. Accordingly, pictures 611, 612, 613, and 614 inlayer N+1 632 have a larger picture size (e.g., larger height and widthand hence more samples) than pictures 615, 616, 617, and 618 in layer N631 in this example. However, such pictures can be separated betweenlayer N+1 632 and layer N 631 by other characteristics. While only twolayers, layer N+1 632 and layer N 631, are shown, a set of pictures canbe separated into any number of layers based on associatedcharacteristics. Layer N+1 632 and layer N 631 may also be denoted by alayer ID. A layer ID is an item of data that is associated with apicture and denotes the picture is part of an indicated layer.Accordingly, each picture 611-618 may be associated with a correspondinglayer ID to indicate which layer N+1 632 or layer N 631 includes thecorresponding picture. For example, a layer ID may include a NAL unitheader layer identifier (nuh_layer_id), which is a syntax element thatspecifies an identifier of a layer that includes a NAL unit (e.g., thatinclude slices and/or parameters of the pictures in a layer). A layerassociated with a lower quality/bitstream size, such as layer N 631, isgenerally assigned a lower layer ID and is referred to as a lower layer.Further, a layer associated with a higher quality/bitstream size, suchas layer N+1 632, is generally assigned a higher layer ID and isreferred to as a higher layer.

Pictures 611-618 in different layers 631-632 are configured to bedisplayed in the alternative. As such, pictures in different layers631-632 can share a temporal ID 622 as long as the pictures are includedin the same AU. A temporal ID 622 is a data element that indicates datacorresponds to temporal location in a video sequence. An AU is a set ofNAL units that are associated with each other according to a specifiedclassification rule and pertain to one particular output time. Forexample, an AU may include one or more pictures in different layers,such as picture 611 and picture 615 when such pictures are associatedwith the same temporal ID 622. As a specific example, a decoder maydecode and display picture 615 at a current display time if a smallerpicture is desired or the decoder may decode and display picture 611 atthe current display time if a larger picture is desired. As such,pictures 611-614 at higher layer N+1 632 contain substantially the sameimage data as corresponding pictures 615-618 at lower layer N 631(notwithstanding the difference in picture size). Specifically, picture611 contains substantially the same image data as picture 615, picture612 contains substantially the same image data as picture 616, etc.

Pictures 611-618 can be coded by reference to other pictures 611-618 inthe same layer N 631 or N+1 632. Coding a picture in reference toanother picture in the same layer results in inter-prediction 623.Inter-prediction 623 is depicted by solid line arrows. For example,picture 613 may be coded by employing inter-prediction 623 using one ortwo of pictures 611, 612, and/or 614 in layer N+1 632 as a reference,where one picture is referenced for unidirectional inter-predictionand/or two pictures are referenced for bidirectional inter-prediction.Further, picture 617 may be coded by employing inter-prediction 623using one or two of pictures 615, 616, and/or 618 in layer N 531 as areference, where one picture is referenced for unidirectionalinter-prediction and/or two pictures are referenced for bidirectionalinter-prediction. When a picture is used as a reference for anotherpicture in the same layer when performing inter-prediction 623, thepicture may be referred to as a reference picture. For example, picture612 may be a reference picture used to code picture 613 according tointer-prediction 623. Inter-prediction 623 can also be referred to asintra-layer prediction in a multi-layer context. As such,inter-prediction 623 is a mechanism of coding samples of a currentpicture by reference to indicated samples in a reference picture that isdifferent from the current picture where the reference picture and thecurrent picture are in the same layer.

Pictures 611-618 can also be coded by reference to other pictures611-618 in different layers. This process is known as inter-layerprediction 621, and is depicted by dashed arrows. Inter-layer prediction621 is a mechanism of coding samples of a current picture by referenceto indicated samples in a reference picture where the current pictureand the reference picture are in different layers and hence havedifferent layer IDs. For example, a picture in a lower layer N 631 canbe used as a reference picture to code a corresponding picture at ahigher layer N+1 632. As a specific example, picture 611 can be coded byreference to picture 615 according to inter-layer prediction 621. Insuch a case, the picture 615 is used as an inter-layer referencepicture. An inter-layer reference picture is a reference picture usedfor inter-layer prediction 621. In most cases, inter-layer prediction621 is constrained such that a current picture, such as picture 611, canonly use inter-layer reference picture(s) that are included in the sameAU and that are at a lower layer, such as picture 615. When multiplelayers (e.g., more than two) are available, inter-layer prediction 621can encode/decode a current picture based on multiple inter-layerreference picture(s) at lower levels than the current picture.

A video encoder can employ a multi-layer video sequence 600 to encodepictures 611-618 via many different combinations and/or permutations ofinter-prediction 623 and inter-layer prediction 621. For example,picture 615 may be coded according to intra-prediction. Pictures 616-618can then be coded according to inter-prediction 623 by using picture 615as a reference picture. Further, picture 611 may be coded according tointer-layer prediction 621 by using picture 615 as an inter-layerreference picture. Pictures 612-614 can then be coded according tointer-prediction 623 by using picture 611 as a reference picture. Assuch, a reference picture can serve as both a single layer referencepicture and an inter-layer reference picture for different codingmechanisms. By coding higher layer N+1 632 pictures based on lower layerN 631 pictures, the higher layer N+1 632 can avoid employingintra-prediction, which has much lower coding efficiency thaninter-prediction 623 and inter-layer prediction 621. As such, the poorcoding efficiency of intra-prediction can be limited to thesmallest/lowest quality pictures, and hence limited to coding thesmallest amount of video data. The pictures used as reference picturesand/or inter-layer reference pictures can be indicated in entries ofreference picture list(s) contained in a reference picture liststructure.

In order to perform such operations, layers such as layer N 631 andlayer N+1 632 may be included in one or more OLSs 625 and 626.Specifically, pictures 611-618 are encoded as layers 631-632 in thebitstream 600, and then each layer 631-632 of pictures is assigned toone or more of the OLSs 625 and 626. The OLS 625 and/or 626 can then beselected and corresponding layers 631 and/or 632 can be transmitted to adecoder, depending on the capabilities at the decoder and/or networkconditions. An OLS 625 is a set of layers for which one or more layersare specified as an output layer. An output layer is a layer that isdesignated for output (e.g., to a display). For example, layer N 631 maybe included solely to support inter-layer prediction 621 and may neverbe output. In such a case, layer N+1 632 is decoded based on layer N 631and is output. In such a case, the OLS 625 includes layer N+1 632 as theoutput layer. When an OLS contains only an output layer, the OLS isreferred to as a 0-th OLS 626. A 0-th OLS 626 is an OLS that containsonly a lowest layer (layer with a lowest layer identifier) and hencecontains only an output layer. In other cases, an OLS 625 may containmany layers in different combinations. For example, an output layer inan OLS 625 can be coded according to inter-layer prediction 621 based ona one, two, or many lower layers. Further, an OLS 625 may contain morethan one output layer. Hence, an OLS 625 may contain one or more outputlayers and any supporting layers needed to reconstruct the outputlayers. While only two OLSs 625 and 626 are shown, a multi-layer videosequence 600 can be coded by employing many different OLSs 625 and/or626 that each employ different combinations of the layers. The OLSs 625and 626 are each associated with an OLS index 629, which is an indexthat uniquely identifies a corresponding OLS 625 and 626.

Checking a multi-layer video sequence 600 for standards conformance at aHRD 500 can become complicated depending on the number of layers 631-632and OLSs 625 and 626. A HRD 500 may segregate the multi-layer videosequence 600 into a sequence of operation points 627 for testing. An OLS625 and/or 626 is identified by an OLS index 629. An operation point 627is a temporal subset of an OLS 625/626. The operation point 627 can beidentified by both the OLS index 629 of the corresponding OLS 625/626 aswell as a highest temporal ID 622. As a specific example, a firstoperation point 627 could include all pictures in a first OLS 625 fromtemporal ID zero to temporal ID two hundred, a second operation point627 could include all pictures in the first OLS 625 from temporal ID twohundred and one to temporal ID four hundred, etc. In such a case, thefirst operation point 627 is described by an OLS index 629 of the firstOLS 625 and a temporal ID of two hundred. Further, the second operationpoint 627 is described by an OLS index 629 of the first OLS 625 and atemporal ID of four hundred. The operation point 627 selected fortesting at a specified instant is referred to as an OP under test(targetOp). Hence, a targetOp is an operation point 627 that is selectedfor conformance testing at a HRD 500.

FIG. 7 is a schematic diagram illustrating an example multi-layer videosequence 700 configured for temporal scalability. The multi-layer videosequence 700 may be encoded by an encoder, such as codec system 200and/or encoder 300 and decoded by a decoder, such as codec system 200and/or decoder 400, for example according to method 100. Further, themulti-layer video sequence 700 can be checked for standard conformanceby a HRD, such as HRD 500. The multi-layer video sequence 700 isincluded to depict another example application for layers in a codedvideo sequence. For example, the multi-layer video sequence 700 may beemployed as a separate embodiment or may be combined with the techniquesdescribed with respect to the multi-layer video sequence 600.

The multi-layer video sequence 700 includes sublayers 710, 720, and 730.A sublayer is a temporal scalable layer of a temporal scalable bitstreamthat includes VCL NAL units (e.g., pictures) with a particular temporalidentifier value as well as associated non-VCL NAL units (e.g.,supporting parameters). For example, a layer, such as a layer N 631and/or layer N+1 632, can be further divided into sublayers 710, 720,and 730 to support temporal scalability. The sublayer 710 may bereferred to as a base layer and sublayers 720 and 730 may be referred toas enhancement layers. As shown, the sublayer 710 includes pictures 711at a first frame rate, such as thirty frames per second. The sublayer710 is a base layer because the sublayer 710 includes the base/lowestframe rate. The sublayer 720 contains pictures 721 that are temporallyoffset from the pictures 711 of sublayer 710. The result is thatsublayer 710 and sublayer 720 can be combined, which results in a framerate that is collectively higher than the frame rate of the sublayer 710alone. For example, sublayer 710 and 720 may have a combined frame rateof sixty frames per second. Accordingly, the sublayer 720 enhances theframe rate of the sublayer 710. Further, sublayer 730 contains pictures731 that are also temporally offset from the pictures 721 and 711 ofsublayers 720 and 710. As such, the sublayer 730 can be combined withsublayers 720 and 710 to further enhance the sublayer 710. For example,the sublayers 710, 720, and 730 may have a combined frame rate of ninetyframes per second.

A sublayer representation 740 can be dynamically created by combiningsublayers 710, 720, and/or 730. A sublayer representation 740 is asubset of a bitstream containing NAL units of a particular sublayer andthe lower sublayers. In the example shown, the sublayer representation740 contains pictures 741, which are the combined pictures 711, 721, and731 of sublayers 710, 720, and 730. Accordingly, the multi-layer videosequence 700 can be temporally scaled to a desired frame rate byselecting a sublayer representation 740 that includes a desired set ofsublayers 710, 720, and/or 730. A sublayer representation 740 may becreated by employing an OLS that includes sublayer 710, 720, and/or 730as layers. In such a case, the sublayer representation 740 is selectedas an output layer. As such, temporal scalability is one of severalmechanisms that can be accomplished using multi-layer mechanisms.

FIG. 8 is a schematic diagram illustrating an example bitstream 800. Forexample, the bitstream 800 can be generated by a codec system 200 and/oran encoder 300 for decoding by a codec system 200 and/or a decoder 400according to method 100. Further, the bitstream 800 may include amulti-layer video sequence 600 and/or 700. In addition, the bitstream800 may include various parameters to control the operation of a HRD,such as HRD 500. Based on such parameters, the HRD can check thebitstream 800 for conformance with standards prior to transmissiontoward a decoder for decoding.

The bitstream 800 includes a VPS 811, one or more SPS 813, a pluralityof picture parameter sets (PPSs) 815, a plurality of slice headers 817,image data 820, and SEI messages 819. A VPS 811 contains data related tothe entire bitstream 800. For example, the VPS 811 may contain datarelated OLSs, layers, and/or sublayers used in the bitstream 800. An SPS813 contains sequence data common to all pictures in a coded videosequence contained in the bitstream 800. For example, each layer maycontain one or more coded video sequences, and each coded video sequencemay reference a SPS 813 for corresponding parameters. The parameters ina SPS 813 can include picture sizing, bit depth, coding tool parameters,bit rate restrictions, etc. It should be noted that, while each sequencerefers to a SPS 813, a single SPS 813 can contain data for multiplesequences in some examples. The PPS 815 contains parameters that applyto an entire picture. Hence, each picture in the video sequence mayrefer to a PPS 815. It should be noted that, while each picture refersto a PPS 815, a single PPS 815 can contain data for multiple pictures insome examples. For example, multiple similar pictures may be codedaccording to similar parameters. In such a case, a single PPS 815 maycontain data for such similar pictures. The PPS 815 can indicate codingtools available for slices in corresponding pictures, quantizationparameters, offsets, etc.

The slice header 817 contains parameters that are specific to each slicein a picture. Hence, there may be one slice header 817 per slice in thevideo sequence. The slice header 817 may contain slice type information,POCs, reference picture lists, prediction weights, tile entry points,deblocking parameters, etc. It should be noted that in some examples, abitstream 800 may also include a picture header, which is a syntaxstructure that contains parameters that apply to all slices in a singlepicture. For this reason, a picture header and a slice header 817 may beused interchangeably in some contexts. For example, certain parametersmay be moved between the slice header 817 and a picture header dependingon whether such parameters are common to all slices in a picture.

The image data 820 contains video data encoded according tointer-prediction and/or intra-prediction as well as correspondingtransformed and quantized residual data. For example, the image data 820may include AUs 821, DUs 822, and/or pictures 823. An AU 821 is a set ofNAL units that are associated with each other according to a specifiedclassification rule and pertain to one particular output time. A DU 822is an AU or a sub-set of an AU and associated non-VCL NAL units. Apicture 823 is an array of luma samples and/or an array of chromasamples that create a frame or a field thereof. In plain language, an AU821 contains various video data that may be displayed at a specifiedinstant in a video sequence as well as supporting syntax data. Hence, anAU 821 may contain a single picture 823 in a single layer bitstream ormultiple pictures from multiple layers that are all associated with thesame instant in a multi-layer bitstream. Meanwhile, a picture 823 is acoded image that may be output for display or used to support coding ofother picture(s) 823 for output. A DU 822 may contain one or morepictures 823 and any supporting syntax data needed for decoding. Forexample, a DU 822 and an AU 821 may be used interchangeably in simplebitstreams (e.g., when an AU contains a single picture). However, inmore complex multi-layer bitstreams, a DU 822 may only contain a portionof the video data from an AU 821. For example, an AU 821 may containpictures 823 at several layers and/or sublayers where some of thepictures 823 are associated with different OLSs. In such a case, a DU822 may only contain picture(s) 823 from a specified OLS and/or aspecified layer/sublayer.

A picture 823 contains one or more slices 825. A slice 825 may bedefined as an integer number of complete tiles or an integer number ofconsecutive complete coding tree unit (CTU) rows (e.g., within a tile)of a picture 823, where the tiles or CTU rows are exclusively containedin a single NAL unit 829. Hence, the slice 825 is also contained in asingle NAL units 829. The slices 825 are further divided into CTUsand/or coding tree blocks (CTBs). A CTU is a group of samples of apredefined size that can be partitioned by a coding tree. A CTB is asubset of a CTU and contains luma components or chroma components of theCTU. The CTUs/CTBs are further divided into coding blocks based oncoding trees. The coding blocks can then be encoded/decoded according toprediction mechanisms.

A bitstream 800 is a sequence of NAL units 829. A NAL unit 829 is acontainer for video data and/or supporting syntax. A NAL unit 829 can bea VCL NAL unit or a non-VCL NAL unit. A VCL NAL unit is a NAL unit 829coded to contain video data, such as a coded slice 825 and an associatedslice header 817. A non-VCL NAL unit is a NAL unit 829 that containsnon-video data such as syntax and/or parameters that support decodingthe video data, performance of conformance checking, or otheroperations. For example, a non-VCL NAL unit can contain a VPS 811, a SPS813, a PPS 815, a SEI message 819, or other supporting syntax.

A SEI message 819 is a syntax structure with specified semantics thatconveys information that is not needed by the decoding process in orderto determine the values of the samples in decoded pictures. For example,the SEI messages may contain data to support HRD processes or othersupporting data that is not directly relevant to decoding the bitstream800 at a decoder. The SEI message 819 may include scalable-nesting SEImessages and/or non-scalable-nested SEI messages. A scalable-nesting SEImessage is a message that contains a plurality of SEI messages thatcorrespond to one or more OLSs or one or more layers. Anon-scalable-nested SEI message is a message that is not nested andhence contains a single SEI message. SEI messages 819 may include a BPSEI message that contains HRD parameters for initializing an HRD tomanage a CPB. SEI messages 819 may also include a PT SEI message thatcontains HRD parameters for managing delivery information for AUs 821 atthe CPB and/or the DPB. SEI messages 819 may also include a DUI SEImessage that contains HRD parameters for managing delivery informationfor DUs 822 at the CPB and/or the DPB.

The bitstream 800 includes an integer number (i) of sets of HRDparameters 833, which are syntax elements that initialize and/or defineoperational conditions of an HRD, such as HRD 500. In some examples, ageneral HRD parameters (general_hrd_parameters) syntax structure maycontain the HRD parameters 833 that apply to all OLSs specified by theVPS 811. In an example, the encoder can encode a video sequence intolayers. The encoder can then encode the HRD parameters 833 into thebitstream 800 to properly configure the HRD to perform conformancechecks. The HRD parameters 833 can also indicate to a decoder that thedecoder is capable of decoding the bitstream 800 according to a deliveryschedule. The HRD parameters 833 can be included in the VPS 811 and/orthe SPS 813. Additional parameters used to configure the HRD may also beincluded in the SEI messages 819.

As noted above, a video stream may include many OLSs and many layers,such as OLS 625, layer N 631, layer N+1 632, sublayer 710, sublayer 720,and/or sublayer 730. Further, some layers may be included in multipleOLSs. As such, a multi-layer video sequence, such as multi-layer videosequence 600 and/or 700, may become quite complicated. This may resultin a complicated HRD checking process at the HRD. Some video codingsystems use a HRD to test the entire bitstream 800 containing amulti-layer video sequence for conformance. The HRD then tests eachlayer/sublayer of the bitstream for conformance. Finally, the HRD checkspotential decodable outputs of the bitstream for conformance, such assublayer representation 740. This approach is complex, redundant, andinvolves the usage of a significant number of HRD parameters 833.

The present disclosure includes mechanisms for a simplified HRDconformance test for use in checking multi-layer bitstreams. Thisapproach reduces the number of HRD parameters 833 in the bitstream 800,and hence decreases the size of the bitstream 800. Further, thisapproach simplifies the HRD process, which saves resources at theencoder/HRD. Specifically, HRD 500 can be configured to only applybitstream conformance tests to each OLS of the bitstream 800 and omittesting of the potential outputs of the OLS and testing of the overallbitstream 800. Each layer than can potentially be decoded and output isincluded in an OLS. Therefore, testing all the OLSs results in thetesting of potential outputs, such as sublayer representation 740, forconformance as part of the OLS conformance checking process. Further,all of the portions of the bitstream 800 that can be sent to a decoderare included in an OLS. As such, testing each OLS for conformanceresults in testing the entire bitstream 800 for conformance.

In a specific example, the VPS 811 may contain a number of OLS 831. Thenumber of OLS 831 specifies the number of OLSs employed in the entirebitstream 800 after encoding and prior to any sub-bitstream extractionprocesses. For example, the number of OLS 831 may be coded as a totalnumber of output layer sets minus one (num_output_layer_sets_minus1)syntax element. The num_output_layer_sets_minus1 plus one specifies thetotal number of OLSs specified by the VPS 811. The minus1 indicates theHRD may add one to the value contained in the syntax element to obtainthe true value. The HRD can read the number of OLS 831 to determine theOLS specified in the VPS 811. The HRD can then check each OP of each OLSbased on the number of OLS 831. As a specific example, the HRD canemploy the number of OLS 831 to sequentially select and test each OLS asa target OLS. When testing an OLS, the HRD can sequentially select andtest each OP of a current OLS as an OP under test (targetOp). This maybe accomplished by selecting a target OLS based on an OP OLS index(opOlsIdx) and a highest OP temporal identifier value (opTid). As such,the bitstream 800 contains various mechanisms that support increasedGradual Decoder Refresh (GDR) functionality, for example with respect toa HRD and/or with respect to a decoder. As such, the mechanismsdescribed with respect to bitstream 800 may increase the functionalityof an encoder and/or decoder. Further, the mechanisms described withrespect to bitstream 800 may support increased coding efficiency and/orsupport the reduction of processor, memory, and/or network communicationresources at the encoder and/or the decoder.

The preceding information is now described in more detail herein below.Layered video coding is also referred to as scalable video coding orvideo coding with scalability. Scalability in video coding may besupported by using multi-layer coding techniques. A multi-layerbitstream comprises a base layer (BL) and one or more enhancement layers(ELs). Examples of scalabilities include spatial scalability,quality/signal to noise ratio (SNR) scalability, multi-view scalability,frame rate scalability, etc. When a multi-layer coding technique isused, a picture or a part thereof may be coded without using a referencepicture (intra-prediction), may be coded by referencing referencepictures that are in the same layer (inter-prediction), and/or may becoded by referencing reference pictures that are in other layer(s)(inter-layer prediction). A reference picture used for inter-layerprediction of the current picture is referred to as an inter-layerreference picture (ILRP). FIG. 6 illustrates an example of multi-layercoding for spatial scalability in which pictures in different layershave different resolutions.

Some video coding families provide support for scalability in separatedprofile(s) from the profile(s) for single-layer coding. Scalable videocoding (SVC) is a scalable extension of the advanced video coding (AVC)that provides support for spatial, temporal, and quality scalabilities.For SVC, a flag is signaled in each macroblock (MB) in EL pictures toindicate whether the EL MB is predicted using the collocated block froma lower layer. The prediction from the collocated block may includetexture, motion vectors, and/or coding modes. Implementations of SVC maynot directly reuse unmodified AVC implementations in their design. TheSVC EL macroblock syntax and decoding process differs from the AVCsyntax and decoding process.

Scalable HEVC (SHVC) is an extension of HEVC that provides support forspatial and quality scalabilities. Multiview HEVC (MV-HEVC) is anextension of HEVC that provides support for multi-view scalability. 3DHEVC (3D-HEVC) is an extension of HEVC that provides support for 3Dvideo coding that is more advanced and more efficient than MV-HEVC.Temporal scalability may be included as an integral part of asingle-layer HEVC codec. In the multi-layer extension of HEVC, decodedpictures used for inter-layer prediction come only from the same AU andare treated as long-term reference pictures (LTRPs). Such pictures areassigned reference indices in the reference picture list(s) along withother temporal reference pictures in the current layer. Inter-layerprediction (ILP) is achieved at the prediction unit (PU) level bysetting the value of the reference index to refer to the inter-layerreference picture(s) in the reference picture list(s). Spatialscalability resamples a reference picture or part thereof when an ILRPhas a different spatial resolution than the current picture beingencoded or decoded. Reference picture resampling can be realized ateither picture level or coding block level.

VVC may also support layered video coding. A VVC bitstream can includemultiple layers. The layers can be all independent from each other. Forexample, each layer can be coded without using inter-layer prediction.In this case, the layers are also referred to as simulcast layers. Insome cases, some of the layers are coded using ILP. A flag in the VPScan indicate whether the layers are simulcast layers or whether somelayers use ILP. When some layers use ILP, the layer dependencyrelationship among layers is also signaled in the VPS. Unlike SHVC andMV-HEVC, VVC may not specify OLSs. An OLS includes a specified set oflayers, where one or more layers in the set of layers are specified tobe output layers. An output layer is a layer of an OLS that is output.In some implementations of VVC, only one layer may be selected fordecoding and output when the layers are simulcast layers. In someimplementations of VVC, the entire bitstream including all layers isspecified to be decoded when any layer uses ILP. Further, certain layersamong the layers are specified to be output layers. The output layersmay be indicated to be only the highest layer, all the layers, or thehighest layer plus a set of indicated lower layers.

Video coding standards may specify a HRD for verifying the conformanceof bitstreams through specified HRD conformance tests. In SHVC andMV-HEVC, three sets of bitstream conformance tests are employed forchecking the conformance of a bitstream. The bitstream is referred to asthe entire bitstream and denoted as entireBitstream. The first set ofbitstream conformance tests are for testing the conformance of theentire bitstream and corresponding temporal subsets. Such tests areemployed regardless of whether there is a layer set specified by theactive VPS that contains all the nuh_layer_id values of VCL NAL unitspresent in the entire bitstream. Accordingly, the entire bitstream isalways checked for conformance even when one or more layers are notincluded in an output set. The second set of bitstream conformance testsare employed for testing the conformance of the layer sets specified bythe active VPS and associated temporal subsets. For all these tests,only the base layer pictures (e.g., pictures with nuh_layer_id equal tozero) are decoded and output. Other pictures are ignored by the decoderwhen the decoding process is invoked. The third set of bitstreamconformance tests are employed for testing the conformance of the OLSsspecified by the VPS extension part of the active VPS and associatedtemporal subsets based on OLSs and bitstream partitions. A bitstreampartition includes one or more layers of an OLS of a multi-layerbitstream.

The preceding aspects contain certain problems. For example, the firsttwo sets of conformance tests may be applied to layers that are notdecoded and not output. For example, layers other than the lowest layermay not be decoded and may not be output. In real applications, adecoder may receive only the data to be decoded. As such, employing thefirst two sets of conformance tests both complicates the codec designand may waste bits for carrying both sequence-level and picture-levelparameters used to support the conformance tests. The third set ofconformance tests involves bitstream partitions. Such partitions mayrelate to one or more layers of an OLS of a multi-layer bitstream. TheHRD may be greatly simplified if conformance tests always operateseparately for each layer instead.

The signaling of sequence-level HRD parameters may be complicated. Forexample, the sequence-level HRD parameters may be signaled in multipleplaces such as both in the SPS and the VPS. Further, the sequence-levelHRD parameters signaling may include redundancy. For example,information that may generally be the same for the entire bitstream canbe repeated at each layer of each OLS. In addition, an example HRDscheme allows a different delivery schedule to be selected for eachlayer. Such delivery schedules may be selected from a list of schedulessignaled for each layer for each operation point where an operationpoint is an OLS or a temporal subset of an OLS. Such a system iscomplicated. Further, an example HRD scheme allows incomplete AUs to beassociated with buffering period SEI messages. An incomplete AU is an AUthat does not have pictures for all the layers present in a CVS.However, HRD initialization at such an AU may be problematic. Forexample, the HRD may not be properly initialized for layers with layeraccess units that are not present in the incomplete AU. In addition, thedemultiplexing process for deriving a layer bitstream may notsufficiently and efficiently remove nested SEI messages that do notapply to the target layer. A layer bitstream occurs when a bitstreampartition contains only one layer. Further, the applicable OLS ofnon-scalable-nested buffering period, picture timing, and decoding unitinformation SEI messages may be specified for the entire bitstream.However, the non-scalable-nested buffering period should instead beapplicable to the 0-th OLS instead.

Further, some VVC implementations may fail to infer HDR parameters whena sub_layer_cpbparams_present_flag is equal to zero. Such an inferencemay enable proper HRD operations. In addition, the values ofbp_max_sub_layers_minus1 and pt_max_sub_layers_minus1 may be required tobe equal to the value of sps_max_sub_layers_minus1. However, thebuffering period and picture timing SEI messages can be nested and canbe applicable to multiple OLSs and multiple layers of each of themultiple OLSs. In such contexts, the layers involved may refer tomultiple SPSs. Hence, the system may have difficulty in tracking whichSPS is the SPS that corresponds to each layer. Therefore, the values ofthese two syntax elements should be constrained based on the value ofvps_max_sub_layers_minus1 instead. Furthermore, since different layersmay have different number of sub-layers, the values of these two syntaxelements may not always be equal to a particular value in all thebuffering period and picture timing SEI messages.

Also, the following problem is associated with the HRD design in bothSHVC/MV-HEVC and VVC. The sub-bitstream extraction process may notremove SEI NAL units containing nested SEI messages that are not neededfor the target OLS.

In general, this disclosure describes approaches for scalable nesting ofSEI messages for output layer sets in multi-layer video bitstreams. Thedescriptions of the techniques are based on VVC. However, the techniquesalso apply to layered video coding based on other video codecspecifications.

One or more of the abovementioned problems may be solved as follows.Specifically, this disclosure includes methods for an HRD design andrelated aspects that allow for efficient signaling of HRD parameterswith much simpler HRD operations compared to SHVC and MV-HEVC. Each ofthe solutions described below corresponds to the problems describedabove. For example, instead of requiring three sets of conformancetests, the present disclosure may only employ one set of conformancetests for testing the conformance of the OLSs specified by the VPS.Further, instead of a design that is based on bitstream partitions, thedisclosed HRD mechanisms may always operate separately for each layer ofan OLS. Further, sequence-level HRD parameters that are global for alllayers and sub-layers of all OLSs may be signaled only once, for examplein the VPS. In addition, a single number of delivery schedules can besignaled for all layers and sub-layers of all OLSs. The same deliveryschedule index can also be applied for all layers in an OLS. Inaddition, incomplete AUs may not be associated with a buffering periodSEI message. An incomplete AU is an AU that does not include picturesfor all the layers present in a CVS. This ensures that the HRD canalways be properly initialized for all layers in an OLS. Also, amechanism is disclosed for efficiently removing nested SEI messages thatdo not apply to the target layer in an OLS. This supports thedemultiplexing process for deriving a layer bitstream. In addition, theapplicable OLS of non-scalable-nested buffering period, picture timing,and decoding unit information SEI messages may be specified to be the0-th OLS. Further, HDR parameters may be inferred whensub_layer_cpb_params_present_flag is equal to 0, which may enable properHRD operations. The values of bp_max_sub_layers_minus1 andpt_max_sub_layers_minus1 may be required to be in the range of zero tovps_max_sub_layers_minus1. In this way, such parameters are not requiredto be a particular value for all the buffering period and picture timingSEI messages. Also, the sub-bitstream extraction process may remove SEINAL units containing nested SEI messages that do not apply to the targetOLS.

An example implementation of the preceding mechanisms is as follows. Anoutput layer is a layer of an output layer set that is output. An OLS isa set of layers including a specified set of layers, where one or morelayers in the set of layers are specified to be output layers. An OLSlayer index is an index, of a layer in an OLS, to the list of layers inthe OLS. A sub-bitstream extraction process is a specified process bywhich NAL units in a bitstream that do not belong to a target set,determined by a target OLS index and a target highest TemporalId, areremoved from the bitstream, with the output sub-bitstream including theNAL units in the bitstream that belong to the target set.

An example video parameter set syntax is as follows.

video_parameter_set_rbsp( ) { Descriptor  ... general_hrd_params_present_flag u(1)  if(general_hrd_params_present_flag ) {   num_units_in_tick u(32)  time_scale u(32)   general_hrd_parameters( )  }  vps_extension_flagu(1)  if( vps_extension_flag )   while( more_rbsp_data( ) )   vps_extension_data_flag u(1)  rbsp_trailing_bits( ) }

An example sequence parameter set RBSP syntax is as follows.

seq_parameter_set_rbsp( ) { Descriptor  sps_decoding_parameter_set_idu(4)  sps_video_parameter_set_id u(4)  sps_max_sub_layers_minus1 u(3) sps_reserved_zero_4bits u(4)  same_nonoutput_level_and_dpb_size_flagu(1)  profile_tier_level( 1, sps_max_sub_layers_minus1 )  if(!same_nonoutput_level_and_dpb_size_flag )   profile_tier_level( 0,sps_max_sub_layers_minus1 )  ...  if( sps_max_sub_layers_minus1 > 0 )  sps_sub_layer_ordering_info_present_flag u(1)  dpb_parameters( 1 ) if( !same_nonoutput_level_and_dpb_size_flag )   dpb_parameters( 0 ) long_term_ref_pics_flag u(1)  ...  sps_scaling_list_enabled_flag u(1) vui_parameters_present_flag u(1)  if( vui_parameters_present_flag )  vui_parameters( )  sps_extension_flag u(1)  if( sps_extension_flag )  while( more_rbsp_data( ) )    sps_extension_data_flag u(1) rbsp_trailing_bits( ) }

An example DPB parameters syntax is as follows.

dpb_parameters( reorderMaxLatencyPresentFlag ) { Descriptor  for( i = (sps_sub_layer_ordering_info_present_flag ? 0 : sps_max_sub_layers_minus1);    i <= sps_max_sub_layers_minus1; i++ ) {  sps_max_dec_pic_buffering_minus1[ i ] ue(v)   if(reorderMaxLatencyPresentFlag ) {    sps_max_num_reorder_pics[ i ] ue(v)   sps_max_latency_increase_plus1[ i ] ue(v)   }  } }

An example general HRD parameters syntax is as follows.

general_hrd_parameters( ) { Descriptor general_nal_hrd_params_present_flag u(1) general_vcl_hrd_params_present_flag u(1)  if(general_nal_hrd_params_present_flag | |general_vcl_hrd_params_present_flag ) {  decoding_unit_hrd_params_present_flag u(1)   if(decoding_unit_hrd_params_present_flag ) {    tick_divisor_minus2 u(8)   decoding_unit_cpb_params_in_pic_timing_sei_flag u(1)   }  bit_rate_scale u(4)   cpb_size_scale u(4)   if(decoding_unit_hrd_params_present_flag )    cpb_size_du_scale u(4)  } if( vps_max_sub_layers_minus1 > 0 )   sub_layer_cpb_params_present_flagu(1)  if( TotalNumOlss > 1 )   num_layer_hrd_params_minus1 ue(v) hrd_cpb_cnt_minus1 ue(v)  for( i = 0; i <= num_layer_hrd_params_minus1;i++ ) {   if( vps_max_sub_layers_minus1 > 0 )    hrd_max_temporal_id[ i] u(3)   layer_level_hrd_parameters( hrd_max_temporal_id[ i ] )  }  if(num_layer_hrd_params_minus1 > 0 )   for( i = 1; i < TotalNumOlss; i++ )   for( j = 0; j < NumLayersInOls[ i ]; j++ )     layer_level_hrd_idx[ i][ j ] ue(v) }

An example video parameter set RBSP semantics is as follows. Theeach_layer_is_an_ols_flag is set equal to one to specify that eachoutput layer set contains only one layer and each layer itself in thebitstream is an output layer set with the single included layer beingthe only output layer. The each_layer_is_an_ols_flag is set equal tozero to specify that an output layer set may contain more than onelayer. If vps_max_layers_minus1 is equal to zero, the value ofeach_layer_is_an_ols_flag is inferred to be equal to one. Otherwise,when vps_all_independent_layers_flag is equal to zero, the value ofeach_layer_is_an_ols_flag is inferred to be equal to zero.

The ols_mode_idc is set equal to zero to specify that the total numberof OLSs specified by the VPS is equal to vps_max_layers_minus1+1, thei-th OLS includes the layers with layer indices from 0 to i, inclusive,and for each OLS only the highest layer in the OLS is output. Theols_mode_idc is set equal to one to specify that the total number ofOLSs specified by the VPS is equal to vps_max_layers_minus1+1, the i-thOLS includes the layers with layer indices from 0 to i, inclusive, andfor each OLS all layers in the OLS are output. The ols_mode_idc is setequal to two to specify that the total number of OLSs specified by theVPS is explicitly signaled and for each OLS the highest layer and anexplicitly signaled set of lower layers in the OLS are output. The valueof ols_mode_idc shall be in the range of zero to two, inclusive. Thevalue three of ols_mode_idc is reserved. Whenvps_all_independent_layers_flag is equal to one andeach_layer_is_an_ols_flag is equal to zero, the value of ols_mode_idc isinferred to be equal to two. The num_output_layer_sets_minus1 plus 1specifies the total number of OLSs specified by the VPS whenols_mode_idc is equal to two.

The variable TotalNumOlss, specifying the total number of OLSs specifiedby the VPS, is derived as follows.

  if( vps_max_layers_minus1 == 0 )  TotalNumOlss = 1 else if(each_layer_is_an_ols_flag || ols_mode_idc == 0 || ols_mode_ide == 1 ) TotalNumOlss = vps_max_layers_minus1 + 1 else if( ols_mode_idc == 2 ) TotalNumOlss = num_output_layer_sets_minus1 + 1

The layer_included_flag[i][j] specifies whether the j-th layer (thelayer with nuh_layer_id equal to vps_layer_id[j]) is included in thei-th OLS when ols_mode_idc is equal to two. Thelayer_included_flag[i][j] is set equal to one to specify that the j-thlayer is included in the i-th OLS. The layer_included_flag[i][j] is setequal to zero to specify the j-th layer is not included in the i-th OLS.

The variable NumLayersInOls[i], specifying the number of layers in thei-th OLS, and the variable LayerIdInOls[i][j], specifying thenuh_layer_id value of the j-th layer in the i-th OLS, are derived asfollows.

  NumLayersInOls[ 0 ] = 1 LayerIdInOls[ 0 ][ 0 ] = vps_layer_id[ 0 ]for( i = 1, i < TotalNumOlss; i++ ) {  if( each_layer_is_an_ols_flag ) {  NumLayersInOls[ i ] = 1   LayerIdInOls[ i ][ 0 ] = vps_layer_id[ i ] } else if( ols_mode_idc == 0 || ols_mode_idc == 1 ) {   NumLayersInOls[i ] = i + 1   for( j = 0; j < NumLayersInOls[ i ]; j++ )   LayerIdInOls[ i ][ j ] = vps_layer_id[ j ]  } else if( ols_mode_idc== 2 ) {   for( k = 0, j = 0; k <= vps_max_layers_minus1; k++ )    if(layer_included_flag[ i ][ k ] )     LayerIdInOls[ i ][ j++ ] =vps_layer_id[ k ]   NumLayersInOls[ i ] = j  } }

The variable OlsLayeIdx[i][j], specifying the OLS layer index of thelayer with nuh_layer_id_equal to LayerldInOls[i][j], is derived asfollows.

  for( i = 0, i < TotalNumOlss; i++ )  for j = 0; j < NumLayersInOls[ i]; j++ )   OlsLayeIdx[ i ][ LayerIdInOls[ i ][ j ] ] = j

The lowest layer in each OLS shall be an independent layer. In otherwords, for each i in the range of zero to TotalNumOlss−1, inclusive, thevalue of vps_independent_layer_flag[GeneralLayerIdx[LayerIdInOls[i][0]]]shall be equal to one. Each layer shall be included in at least one OLSspecified by the VPS. In other words, for each layer with a particularvalue of nuh_layer_id nuhLayerId, equal to one of vps_layer_id[k] for kin the range of zero to vps_max_layers_minus1, inclusive, there shall beat least one pair of values of i and j, where i is in the range of zeroto TotalNumOlss−1, inclusive, and j is in the range ofNumLayersInOls[i]−1, inclusive, such that the value ofLayerIdInOls[i][j] is equal to nuhLayerId. Any layer in an OLS shall bean output layer of the OLS or a (direct or indirect) reference layer ofan output layer of the OLS.

The vps_output_layer_flag[i][j] specifies whether the j-th layer in thei-th OLS is output when ols_mode_idc is equal to two. Thevps_output_layer_flag[i] equal to one specifies that the j-th layer inthe i-th OLS is output. The vps_output_layer_flag[i] is set equal tozero to specify that the j-th layer in the i-th OLS is not output. Whenvps_all_independent_layers_flag is equal to one andeach_layer_is_an_ols_flag is equal to zero, the value ofvps_output_layer_flag[i] is inferred to be equal to one. The variableOutputLayerFlag[i][j], for which the value one specifies that the j-thlayer in the i-th OLS is output and the value zero specifies that thej-th layer in the i-th OLS is not output, is derived as follows.

  for( i = 0, i < TotalNumOlss; i++ ) {  OutputLayerFlag[ i ][NumLayersInOls[ i ] − 1 ] = 1  for( j = 0; j < NumLayersInOls[ i ] − 1;j++ )   if( ols_mode_idc[ i ] == 0 )    OutputLayerFlag[ i ][ j ] = 0  else if( ols_mode_idc[ i ] == 1 )    OutputLayerFlag[ i ][ j ] = 1  else if( ols_mode_idc[ i ] == 2 )    OutputLayerFlag[ i ][ j ]=vps_output_layer_flag[ i ][ j ] }The 0-th OLS contains only the lowest layer (the layer with nuh_layer_idequal to vps_layer_id[0]) and for the 0-th OLS the only included layeris output.

The vps_extension_flag is set equal to zero to specify that novps_extension_data_flag syntax elements are present in the VPS RBSPsyntax structure. The vps_extension_flag is set equal to one to specifythat there are vps_extension_data_flag syntax elements present in theVPS RBSP syntax structure. The vps_extension_data_flag may have anyvalue. The presence and value of the vps_extension_data_flag do notaffect decoder conformance to specified profiles. Decoders shall ignoreall vps_extension_data_flag syntax elements.

An example DPB parameters semantics is as follows. The dpb_parameters( )syntax structure provides DPB size information, and, optionally, maximumpicture reorder number and maximum latency (MRML) information. Each SPSincludes one or dpb_parameters( )syntax structures. The firstdpb_parameters( ) syntax structure in an SPS contains both DPB sizeinformation and MRML information. When present, the seconddpb_parameters( ) syntax structure in an SPS contains DPB sizeinformation only. The MRML information in the first dpb_parameters( )syntax structure in an SPS applies to a layer referring to the SPSregardless of whether the layer is an output layer in an OLS. The DPBsize information in the first dpb_parameters( ) syntax structure in anSPS applies to a layer referring to the SPS when the layer is an outputlayer of an OLS. The DPB size information included in the seconddpb_parameters( ) syntax structure, when present, in an SPS applies to alayer referring to the SPS when the layer is a non-output layer of anOLS. When an SPS includes only one dpb_parameters( ) syntax structure,the DPB size information for the layer as a non-output layer is inferredto be the same as that for the layer as an output layer.

An example general HRD parameters semantics is as follows. Thegeneral_hrd_parameters( ) syntax structure provides HRD parameters usedin the HRD operations. The sub_layer_cpb_params_present_flag is setequal to one to specify that the i-th layer_level_hrd_parameters( )syntax structure contains HRD parameters for the sub-layerrepresentations with TemporalId in the range of zero tohrd_max_temporal_id[i], inclusive. The sub_layer_cpbparams_present_flagis set equal to zero to specify that the i-thlayer_level_hrd_parameters( ) syntax structure contains HRD parametersfor the sub-layer representation with TemporalId equal tohrd_max_temporal_id[i] only. When vps_max_sub_layers_minus1 is equal tozero, the value of sub_layer_cpb_params_present_flag is inferred to beequal to zero. When sub_layer_cpb_params_present_flag is equal to zero,the HRD parameters for the sub-layer representations with TemporalId inthe range of zero to hrd_max_temporal_id[i]−1, inclusive, are inferredto be the same as that for the sub-layer representation with TemporalIdequal to hrd_max_temporal_id[i]. These include the HRD parametersstarting from the fixed_pic_rate_general_flag[i] syntax element till thesub_layer_hrd_parameters(i) syntax structure immediately under thecondition if (general_vcl_hrd_params_present_flag) in thelayer_level_hrd_parameters syntax structure. Thenumlayer_hrd_params_minus1 plus one specifies the number oflayer_level_hrd_parameters( ) syntax structures present in thegeneral_hrd_parameters( ) syntax structure. The value ofnum_layer_hrd_params_minus1 shall be in the range of zero to sixtythree, inclusive. The hrd_cpb_cnt_minus1 plus one specifies the numberof alternative CPB specifications in the bitstream of the CVS. The valueof hrd_cpb_cnt_minus1 shall be in the range of zero to thirty one,inclusive. The hrd_max_temporal_id[i] specifies the TemporalId of thehighest sub-layer representation for which the HRD parameters arecontained in the i-th layer_level_hrd_parameters( ) syntax structure.The value of hrd_max_temporal_id[i] shall be in the range of zero tovps_max_sub_layers_minus1, inclusive. When vps_max_sub_layers_minus1 isequal to zero, the value of hrd_max_temporal_id[i] is inferred to beequal to zero. The layer_level_hrd_idx[i][j] specifies the index of thelayer_level_hrd_parameters( ) syntax structure that applies to the j-thlayer in the i-th OLS. The value of layer_level_hrd_idx[[i][j] shall bein the range of zero to num_layer_hrd_params_minus1, inclusive. When notpresent, the value of layer_level_hrd_idx[[0][0] is inferred to be equalto zero.

An example sub-bitstream extraction process is as follows. Inputs tothis process are a bitstream inBitstream, a target OLS indextargetOlsIdx, and a target highest TemporalId value tIdTarget. Output ofthis process is a sub-bitstream outBitstream. It is a requirement ofbitstream conformance for the input bitstream that any outputsub-bitstream that is the output of the process specified in this clausewith the bitstream, targetOlsIdx equal to an index to the list of OLSsspecified by the VPS, and tIdTarget equal to any value in the range ofzero to six, inclusive, as inputs, and that satisfies the followingconditions shall be a conforming bitstream. The output sub-bitstreamshould contain at least one VCL NAL unit with nuh_layer_id equal to eachof the nuh_layer_id values in LayerIdInOls[targetOlsIdx]. The outputsub-bitstream should contain at least one VCL NAL unit with TemporalIdequal to tIdTarget. A conforming bitstream contains one or more codedslice NAL units with Temporalld equal to zero, but does not have tocontain coded slice NAL units with nuh_layer_id equal to zero.

The output sub-bitstream OutBitstream is derived as follows. Thebitstream outBitstream is set to be identical to the bitstreaminBitstream. Remove from outBitstream all NAL units with TemporalIdgreater than tIdTarget. Remove from outBitstream all NAL units withnuh_layer_id not included in the list LayerIdInOls[ targetOlsIdx].Remove from outBitstream all SEI NAL units that contain a scalablenesting SEI message that has nesting_ols_flag equal to one and there isno value of i in the range of zero to nesting_num_olss_minus1,inclusive, such that NestingOlsIdx[i] is equal to targetOlsIdx. WhentargetOlsIdx is greater than zero, remove from outBitstream all SEI NALunits that contain a non-scalable-nested SEI message with payloadTypeequal to zero (buffering period), one (picture timing), or one hundredthirty (decoding unit information).

An example HRD general aspects is as follows. This section specifies theHRD and its use to check bitstream and decoder conformance. A set ofbitstream conformance tests is employed for checking the conformance ofa bitstream, which is referred to as the entire bitstream, denoted asentireBitstream. The set of bitstream conformance tests are for testingthe conformance of each OLS specified by the VPS and the temporalsubsets of each OLS. For each test, the following ordered steps apply inthe order listed.

An operation point under test, denoted as targetOp, is selected byselecting a target OLS with OLS index opOlsIdx and a highest TemporalIdvalue opTid. The value of opOlsIdx is in the range of zero toTotalNumOlss−one, inclusive. The value of opTid is in the range of zeroto vps_maxsub_layers_minus 1, inclusive. The values of opOlsIdx andopTid are such that the sub-bitstream BitstreamToDecode that is theoutput by invoking the sub-bitstream extraction process withentireBitstream, opOlsIdx, and opTid as inputs satisfy the followingconditions. There is at least one VCL NAL unit with nuhlayer_id equal toeach of the nuh_layer_id values in LayerIdInOls[opOlsIdx] inBitstreamToDecode. There is at least one VCL NAL unit with TemporalIdequal to opTid in BitstreamToDecode.

The values of TargetOlsIdx and Htid are set equal to opOlsIdx and opTid,respectively, of targetOp. A value of ScIdx is selected. The selectedScIdx shall be in the range of zero to hrd_cpb_cnt_minus1, inclusive. Anaccess unit in BitstreamToDecode associated with buffering period SEImessages (present in TargetLayerBitstream or available through anexternal mechanism not specified in this Specification) applicable toTargetOlsIdx is selected as the HRD initialization point and referred toas access unit zero for each layer in the target OLS.

The subsequent steps apply to each layer with OLS layer indexTargetOlsLayerIdx in the target OLS. If there is only one layer in thetarget OLS, the layer bitstream under test TargetLayerBitstream is setidentical to BitstreamToDecode. Otherwise, TargetLayerBitstream isderived by invoking the demultiplexing process for deriving a layerbitstream with BitstreamToDecode, TargetOlsIdx, and TargetOlsLayerIdx asinputs and the output is assigned to TargetLayerBitstream.

The layer_level_hrd_parameters( ) syntax structure and thesub_layer_hrd_parameters( ) syntax structure applicable toTargetLayerBitstream are selected as follows. Thelayer_level_hrd_idx[TargetOlsIdx][TargetOlsLayerIdx]-thlayer_level_hrd_parameters( ) syntax structure in the VPS (or providedthrough an external mechanism such as user input) is selected. Withinthe selected layer_level_hrd_parameters( ) syntax structure, ifBitstreamToDecode is a Type I bitstream, thesub_layer_hrd_parameters(Htid) syntax structure that immediately followsthe condition if (general_vcl_hrd_params_present_flag) is selected andthe variable NalHrdModeFlag is set equal to zero. Otherwise(BitstreamToDecode is a Type II bitstream), thesub_layer_hrd_parameters(Htid) syntax structure that immediately followseither the condition if (general_vcl_hrd_params_present_flag) (in thiscase the variable NalHrdModeFlag is set equal to zero) or the conditionif (general_nal_hrd_params_present_flag) (in this case the variableNalHrdModeFlag is set equal to one) is selected. When BitstreamToDecodeis a Type II bitstream and NalHrdModeFlag is equal to zero, all non-VCLNAL units except filler data NAL units, and all leading_zero_8bits,zero_byte, start_codeprefix_one_3bytes, and trailing_zero_8bits syntaxelements that form a byte stream from the NAL unit stream, when present,are discarded from TargetLayerBitstream and the remaining bitstream isassigned to TargetLayerBitstream.

When decoding_unit_hrd_params_present_flag is equal to one, the CPB isscheduled to operate either at the access unit level (in which case thevariable DecodingUnitHrdFlag is set equal to zero) or at the decodingunit level (in which case the variable DecodingUnitHrdFlag is set equalto one). Otherwise, DecodingUnitHrdFlag is set equal to zero and the CPBis scheduled to operate at the access unit level. For each access unitin TargetLayerBitstream starting from access unit zero, the bufferingperiod SEI message (present in TargetLayerBitstream or available throughan external mechanism) that is associated with the access unit andapplies to TargetOlsIdx and TargetOlsLayerIdx is selected, the picturetiming SEI message (present in TargetLayerBitstream or available throughan external mechanism) that is associated with the access unit andapplies to TargetOlsIdx and TargetOlsLayerIdx is selected, and whenDecodingUnitHrdFlag is equal to one anddecoding_unit_cpbparams_inpic_timing_sei_flag is equal to zero, thedecoding unit information SEI messages (present in TargetLayerBitstreamor available through an external mechanism) that are associated withdecoding units in the access unit and apply to TargetOlsIdx andTargetOlsLayerIdx are selected.

Each conformance test includes a combination of one option in each ofthe above steps. When there is more than one option for a step, for anyparticular conformance test only one option is chosen. All possiblecombinations of all the steps form the entire set of conformance tests.For each operation point under test, the number of bitstream conformancetests to be performed is equal to n0*n1*n2*n3, where the values of n0,n1, n2, and n3 are specified as follows. n1 is equal tohrd_cpb_cnt_minus1+1. n1 is the number of access units inBitstreamToDecode that are associated with buffering period SEImessages. n2 is derived as follows. If BitstreamToDecode is a Type Ibitstream, n0 is equal to one. Otherwise (BitstreamToDecode is a Type IIbitstream), n0 is equal to two. n3 is derived as follows. Ifdecoding_unit_hrd_params_present_flag is equal to zero, n3 is equal toone. Otherwise, n3 is equal to two.

The HRD contains a bitstream demultiplexer (optionally present), a codedpicture buffer (CPB) for each layer, an instantaneous decoding processfor each layer, a decoded picture buffer (DPB) that contains a sub-DPBfor each layer, and output cropping.

In an example, the HRD operates as follows. The HRD is initialized atdecoding unit zero, with each CPB and each sub-DPB of the DPB set to beempty. The sub-DPB fullness for each sub-DPB is set equal to zero. Afterinitialization, the HRD is not initialized again by subsequent bufferingperiod SEI messages. Data associated with decoding units that flow intoeach CPB according to a specified arrival schedule are delivered by theHSS. The data associated with each decoding unit are removed and decodedinstantaneously by the instantaneous decoding process at the CPB removaltime of the decoding unit. Each decoded picture is placed in the DPB. Adecoded picture is removed from the DPB when it becomes no longer neededfor inter prediction reference and no longer needed for output.

In an example, the demultiplexing process for deriving a layer bitstreamis as follows. Inputs to this process are a bitstream inBitstream, atarget OLS index targetOlsIdx, and a target OLS layer indextargetOlsLayerIdx. Output of this process is a layer bitstreamoutBitstream. The output layer bitstream outBitstream is derived asfollows. The bitstream outBitstream is set to be identical to thebitstream inBitstream. Remove from outBitstream all NAL units withnuhlayer_id not equal to LayerIdInOls[targetOlsIdx][targetOlsLayerIdx].Remove from outBitstream all SEI NAL units that contain a scalablenesting SEI message that has nesting_ols_flag equal to one and there areno values of i and j in the range of zero to nesting_num_olss_minus1,inclusive, and zero to nesting_num_ols_layers_minus1[i], inclusive,respectively, such that NestingOlsLayerIdx[i][j] is equal totargetOlsLayerIdx. Remove from outBitstream all SEI NAL units thatcontain a scalable nesting SEI message that has nesting_ols_flag equalto one and there are values of i and j in the range of zero tonesting_num_olss_minus1, inclusive, and zero tonesting_num_ols_layers_minus1[i], inclusive, respectively, such thatNestingOlsLayerIdx[i][j] is less than targetOlsLayerIdx. Remove fromoutBitstream all SEI NAL units that contain a scalable nesting SEImessage that has nesting_ols_flag equal to zero and there is no value ofi in the range of zero to NestingNumLayers−1, inclusive, such thatNestingLayerId[i] is equal toLayerIdInOls[targetOlsIdx][targetOlsLayerIdx]. Remove from outBitstreamall SEI NAL units that contain a scalable nesting SEI message that hasnesting_ols_flag equal to zero and there is at least one value of i inthe range of zero to NestingNumLayers−1, inclusive, such thatNestingLayerId[i] is less thanLayerIdInOls[targetOlsIdx][targetOlsLayerIdx].

An example buffering period SEI message syntax is as follows.

buffering_period( payloadSize ) { Descriptor  ... bp_max_sub_layers_minus1 u(3)  bp_cpb_cnt_minus1 ue(v)  ... }

An example scalable nesting SEI message syntax is as follows.

scalable_nesting( payloadSize ) { Descriptor  nesting_ols_flag u(1)  if(nesting_ols_flag ) {   nesting_num_olss_minus1 ue(v)   for( i = 0; i <=nesting_num_olss_minus1; i++ ) {    nesting_ols_idx_delta_minus1[ i ]ue(v)    if( NumLayersInOls[ NestingOlsIdx[ i ] ] > 1 ) {    nesting_num_ols_layers_minus1[ i ] ue(v)     for( j = 0; j <=nesting_num_ols_layers_minus1[ i ]; j++ )     nesting_ols_layer_idx_delta_minus1[ i ][ j ] ue(v)    }   }  } else{   nesting_all_layers_flag u(1)   if( !nesting_all_layers_flag ) {   nesting_num_layers_minus1 ue(v)    for( i = 1; i <=nesting_num_layers_minus1; i++ )     nesting_layer_id[ i ] u(6)   }  } nesting_num_seis_minus1 ue(v)  while( !byte_aligned( ) )  nesting_zero_bit /* equal to 0 */ u(1)  for( i = 0; i <=nesting_num_seis_minus1; i++)   sei_message( ) }

An example general SEI payload semantics is as follows. The followingapplies on the applicable layers (in the context of an OLS or generally)of non-scalable-nested SEI messages. For a non-scalable-nested SEImessage, when payloadType is equal to zero (buffering period), one(picture timing), or one hundred thirty (decoding unit information), thenon-scalable-nested SEI message applies only to the lowest layer in thecontext of the 0-th OLS. For a non-scalable-nested SEI message, whenpayloadType is equal to any value among VclAssociatedSeiList, thenon-scalable-nested SEI message applies only to the layer for which theVCL NAL units have nuh_layer_id equal to the nuh_layer_id of the SEI NALunit containing the SEI message.

An example buffering period SEI message semantics is as follows. Abuffering period SEI message provides initial CPB removal delay andinitial CPB removal delay offset information for initialization of theHRD at the position of the associated access unit in decoding order.When the buffering period SEI message is present, a picture is said tobe a notDiscardablePic picture when the picture has TemporalId equal tozero and is not a RASL or random access decodable leading (RADL)picture. When the current picture is not the first picture in thebitstream in decoding order, let prevNonDiscardablePic be the precedingpicture in decoding order with TemporalId equal to zero that is not aRASL or RADL picture.

The presence of buffering period SEI messages is specified as follows.If NalHrdBpPresentFlag is equal to one or VclHrdBpPresentFlag is equalto one, the following applies for each access unit in the CVS. If theaccess unit is an IRAP or GDR access unit, a buffering period SEImessage applicable to the operation point shall be associated with theaccess unit. Otherwise, if the access unit contains a notDiscardablePic,a buffering period SEI message applicable to the operation point may ormay not be associated with the access unit. Otherwise, the access unitshall not be associated with a buffering period SEI message applicableto the operation point. Otherwise (NalHrdBpPresentFlag andVclHrdBpPresentFlag are both equal to zero), no access unit in the CVSshall be associated with a buffering period SEI message. For someapplications, frequent presence of buffering period SEI messages may bedesirable (e.g., for random access at an TRAP picture or a non-IRAPpicture or for bitstream splicing). When a picture in an access unit isassociated with a buffering period SEI message, the access unit shallhave a picture in each of the layers present in the CVS, and eachpicture in the access unit shall be with a buffering period SEI message.

The bp_max_sub_layers_minus1 plus 1 specifies the maximum number oftemporal sub-layers for which CPB removal delay and CBP removal offsetare indicated in the buffering period SEI message. The value ofbp_max_sub_layers_minus1 shall be in the range of zero tovps_max_sub_layers_minus1, inclusive. The bp_cpb_cnt_minus1 plus 1specifies the number of syntax element pairsnal_initial_cpb_removal_delay[i][j] andnal_initial_cpb_removal_offset[i][j] of the i-th temporal sub-layer whenbp_nal_hrd_params_present_flag is equal to one, and the number of syntaxelement pairs vcl_initial_cpb_removal_delay[i][j] andvcl_initial_cpb_removal_offset[i][j] of the i-th temporal sub-layer whenbp_vcl_hrd_params_present_flag is equal to one. The value ofbp_cpb_cnt_minus1 shall be in the range of zero to thirty one,inclusive. The value of bp_cpb_cnt_minus1 shall be equal to the value ofhrd_cpb_cnt_minus1.

An example picture timing SEI message semantics is as follows. Thepicture timing SEI message provides CPB removal delay and DPB outputdelay information for the access unit associated with the SEI message.If bp_nal_hrd_params_present_flag or bp_vcl_hrd_params_present_flag ofthe buffering period SEI message applicable for the current access unitis equal to one, the variable CpbDpbDelaysPresentFlag is set equal toone. Otherwise, CpbDpbDelaysPresentFlag is set equal to zero. Thepresence of picture timing SEI messages is specified as follows. IfCpbDpbDelaysPresentFlag is equal to one, a picture timing SEI messageshall be associated with the current access unit. Otherwise(CpbDpbDelaysPresentFlag is equal to zero), there shall not be a picturetiming SEI message associated with the current access unit. TheTemporalId in the picture timing SEI message syntax is the TemporalId ofthe SEI NAL unit containing the picture timing SEI message. Thept_max_sub_layers_minus1 plus 1 specifies the TemporalId of the highestsub-layer representation for which the CPB removal delay information iscontained in the picture timing SEI message. The value ofpt_max_sub_layers_minus1 shall be in the range of zero tovps_max_sub_layers_minus1, inclusive.

An example scalable nesting SEI message semantics is as follows. Thescalable nesting SEI message provides a mechanism to associate SEImessages with specific layers in the context of specific OLSs or withspecific layers not in the context of an OLS. A scalable nesting SEImessage contains one or more SEI messages. The SEI messages contained inthe scalable nesting SEI message are also referred to as thescalable-nested SEI messages. It is a requirement of bitstreamconformance that the following restrictions apply on containing of SEImessages in a scalable nesting SEI message. An SEI message that haspayloadType equal to one hundred thirty two (decoded picture hash) orone hundred thirty three (scalable nesting) shall not be contained in ascalable nesting SEI message. When a scalable nesting SEI messagecontains a buffering period, picture timing, or decoding unitinformation SEI message, the scalable nesting SEI message shall notcontain any other SEI message with payloadType not equal to zero(buffering period), one (picture timing), or one hundred thirty(decoding unit information).

It is a requirement of bitstream conformance that the followingrestrictions apply on the value of the nal_unit_type of the SEI NAL unitcontaining a scalable nesting SEI message. When a scalable nesting SEImessage contains an SEI message that has payloadType equal to zero(buffering period), one (picture timing), one hundred thirty (decodingunit information), one forty five (dependent RAP indication), or onehundred sixty eight (frame-field information), the SEI NAL unitcontaining the scalable nesting SEI message shall have nal_unit_typeequal to PREFIX_SEI_NUT. When a scalable nesting SEI message contains anSEI message that has payloadType equal to one hundred thirty two(decoded picture hash), the SEI NAL unit containing the scalable nestingSEI message shall have nal_unit_type equal to SUFFIX_SEI_NUT.

The nesting_ols_flag is set to one to specify that the scalable-nestedSEI messages apply to specific layers in the context of specific OLSs.The nesting_ols_flag is set to zero to specify that the scalable-nestedSEI messages generally apply (not in the context of an OLS) to specificlayers. It is a requirement of bitstream conformance that the followingrestrictions apply on the value of nesting_ols_flag. When the scalablenesting SEI message contains an SEI message that has payloadType equalto zero (buffering period), one (picture timing), or one hundred thirty(decoding unit information), the value of nesting_ols_flag shall beequal to one. When the scalable nesting SEI message contains an SEImessage that has payloadType equal to a value in VclAssociatedSeiList,the value of nesting_ols_flag shall be equal to zero. Thenesting_num_olss_minus1 plus 1 specifies the number of OLSs to which thescalable-nested SEI messages apply. The value of nesting_num_olss_minus1shall be in the range of zero to TotalNumOlss−1, inclusive. Thenesting_ols_idx_delta_minus1[i] is used to derive the variableNestingOlsIdx[i] that specifies the OLS index of the i-th OLS to whichthe scalable-nested SEI messages apply when nesting_ols_flag is equal toone. The value of nesting_ols_idx_delta_minus1[i] shall be in the rangeof zero to TotalNumOlss minus two, inclusive. The variableNestingOlsIdx[i] is derived as follows:

  if( i == 0 )  NestingOlsIdx[ i ] = nesting_ols_idx_delta_minus1[ i]   (D-2) else  NestingOlsIdx[ i ] = NestingOlsIdx[ i − 1 ] + nesting_ols_idx_delta_minus1[ i ] + 1

The nesting_num_ols_layers_minus1[i] plus 1 specifies the number oflayers to which the scalable-nested SEI messages apply in the context ofthe NestingOlsIdx[i]-th OLS. The value ofnesting_num_ols_layers_minus1[i] shall be in the range of zero toNumLayersInOls[NestingOlsIdx[i]]−1, inclusive. Thenesting_ols_layer_idx_delta minus1[i][j] is used to derive the variableNestingOlsLayerIdx[i][j] that specifies the OLS layer index of the j-thlayer to which the scalable-nested SEI messages apply in the context ofthe NestingOlsIdx[i]-th OLS when nesting_ols_flag is equal to one. Thevalue of nesting_ols_layer_idx_delta minus1[i] shall be in the range ofzero to NumLayersInOls[nestingOlsIdx[i]] minus two, inclusive. Thevariable NestingOlsLayerIdx[i][j] is derived as follows:

if(j == 0 )  NestingOlsLayerIdx[ i ][ j ] =               (D-2) nesting_ols_layer_idx_delta_minus1[ i ][ j ] else  NestingOlsLayerIdx[i ][ j ] = NestingOlsLayerIdx[ i ][ j − 1 ] +  nesting_ols_layer_idx_delta_minus1[ i ][ j ] + 1

The lowest value among all values of LayerIdInOls[NestingOlsIdx[i]][NestingOlsLayerIdx[i][0]] for i in the range of zero tonesting_num_olss_minus1, inclusive, shall be equal to nuhlayer_id of thecurrent SEI NAL unit (the SEI NAL unit containing the scalable nestingSEI message). The nesting_all_layers_flag is set to one to specify thatthe scalable-nested SEI messages generally apply to all layers that havenuh_layer_id greater than or equal to the nuh_layer_id of the currentSEI NAL unit. The nesting_all_layers_flag is set to zero to specify thatthe scalable-nested SEI messages may or may not generally apply to alllayers that have nuhlayer_id greater than or equal to the nuh_layer_idof the current SEI NAL unit. The nesting_num_layers_minus1 plus 1specifies the number of layers to which the scalable-nested SEI messagesgenerally apply. The value of nesting_num_layers_minus1 shall be in therange of zero to vps_max_layers_minus1−GeneralLayerIdx[nuh_layer_id],inclusive, where nuhlayer_id is the nuh_layer_id of the current SEI NALunit. The nesting_layer_id[i] specifies the nuh_layer_id value of thei-th layer to which the scalable-nested SEI messages generally applywhen nesting_all_layers_flag is equal to zero. The value ofnesting_layer_id[i] shall be greater than nuhlayer_id, wherenuh_layer_id is the nuh_layer_id of the current SEI NAL unit. Whennesting_ols_flag is equal to zero, the variable NestingNumLayers,specifying the number of layer(s) to which the scalable-nested SEImessages generally apply, and the list NestingLayerId[i] for i in therange of zero to NestingNumLayers−1, inclusive, specifying the list ofnuhlayer_id value of the layers to which the scalable-nested SEImessages generally apply, are derived as follows, where nuh_layer_id isthe nuh_layer_id of the current SEI NAL unit.

if( nesting_all_layers_flag ) {  NestingNumLayers =vps_max_layers_minus1 + 1 − GeneralLayerIdx[ nuh_layer_id ]  for( i = 0;i < NestingNumLayers; i ++)   NestingLayerId[ i ] =   vps_layer_id[GeneralLayerIdx[ nuh_layer_id ] + i ] } else{                         (D-2)  NestingNumLayers =nesting_num_layers_minus1 + 1  for( i = 0; i < NestingNumLayers; i ++)  NestingLayerId[ i ] = ( i == 0 ) ? nuh_layer_id : nesting_layer_id[ i] }

The nesting_num_seis_minus1 plus one specifies the number ofscalable-nested SEI messages. The value of nesting_num_seis_minus1 shallbe in the range of zero to sixty three, inclusive. The nesting_zero_bitshall be equal to zero.

FIG. 9 is a schematic diagram of an example video coding device 900. Thevideo coding device 900 is suitable for implementing the disclosedexamples/embodiments as described herein. The video coding device 900comprises downstream ports 920, upstream ports 950, and/or transceiverunits (Tx/Rx) 910, including transmitters and/or receivers forcommunicating data upstream and/or downstream over a network. The videocoding device 900 also includes a processor 930 including a logic unitand/or central processing unit (CPU) to process the data and a memory932 for storing the data. The video coding device 900 may also compriseelectrical, optical-to-electrical (OE) components, electrical-to-optical(EO) components, and/or wireless communication components coupled to theupstream ports 950 and/or downstream ports 920 for communication of datavia electrical, optical, or wireless communication networks. The videocoding device 900 may also include input and/or output (I/O) devices 960for communicating data to and from a user. The I/O devices 960 mayinclude output devices such as a display for displaying video data,speakers for outputting audio data, etc. The I/O devices 960 may alsoinclude input devices, such as a keyboard, mouse, trackball, etc.,and/or corresponding interfaces for interacting with such outputdevices.

The processor 930 is implemented by hardware and software. The processor930 may be implemented as one or more CPU chips, cores (e.g., as amulti-core processor), field-programmable gate arrays (FPGAs),application specific integrated circuits (ASICs), and digital signalprocessors (DSPs). The processor 930 is in communication with thedownstream ports 920, Tx/Rx 910, upstream ports 950, and memory 932. Theprocessor 930 comprises a coding module 914. The coding module 914implements the disclosed embodiments described herein, such as methods100, 1000, and 1100, which may employ a multi-layer video sequence 600,a multi-layer video sequence 700, and/or a bitstream 800. The codingmodule 914 may also implement any other method/mechanism describedherein. Further, the coding module 914 may implement a codec system 200,an encoder 300, a decoder 400, and/or a HRD 500. For example, the codingmodule 914 may be employed to implement a HRD. Further, the codingmodule 914 may be employed to encode parameters into a bitstream tosupport HRD conformance checking processes. Accordingly, the codingmodule 914 may be configured to perform mechanisms to address one ormore of the problems discussed above. Hence, coding module 914 causesthe video coding device 900 to provide additional functionality and/orcoding efficiency when coding video data. As such, the coding module 914improves the functionality of the video coding device 900 as well asaddresses problems that are specific to the video coding arts. Further,the coding module 914 effects a transformation of the video codingdevice 900 to a different state. Alternatively, the coding module 914can be implemented as instructions stored in the memory 932 and executedby the processor 930 (e.g., as a computer program product stored on anon-transitory medium).

The memory 932 comprises one or more memory types such as disks, tapedrives, solid-state drives, read only memory (ROM), random access memory(RAM), flash memory, ternary content-addressable memory (TCAM), staticrandom-access memory (SRAM), etc. The memory 932 may be used as anover-flow data storage device, to store programs when such programs areselected for execution, and to store instructions and data that are readduring program execution

FIG. 10 is a flowchart of an example method 1000 of encoding a videosequence to support performance of bitstream conformance tests for anOLS. Method 1000 may be employed by an encoder, such as a codec system200, an encoder 300, and/or a video coding device 900 when performingmethod 100. Further, the method 1000 may operate on a HRD 500 and hencemay perform conformance tests on a multi-layer video sequence 600, amulti-layer video sequence 700, and/or a bitstream 800.

Method 1000 may begin when an encoder receives a video sequence anddetermines to encode that video sequence into a multi-layer bitstream,for example based on user input. At step 1001, the encoder encodes abitstream. The bitstream comprises one or more OLSs. Each OLS is a setof layers for which one or more of the layers are specified as outputlayers.

At step 1003, the encoder encodes a VPS into the bitstream. The VPS isencoded including data specifying the OLSs. Specifically, the VPS caninclude data describing the OLS generated as part of encoding thebitstream at step 1001. For example, the VPS may include a total numberof output layer sets minus one (num_output_layer_sets_minus1) plus onethat specifies a total number of OLSs specified by the VPS. The encodercan then forward the bitstream toward a HRD. For example, the encodercan operate on a first processor and the HRD can operate on a secondprocessor for example on the same computer chassis or in the samenetwork. Alternatively, the encoder and HRD can operate on the sameprocessor or set of processor, for example via a multi-threadingmechanism. This allows a set of bitstream conformance tests to beperformed by a HRD operating on the processor(s). In order to supportsuch HRD tests, the encoder can encode a set of HRD parameters into theVPS at step 1003. For example, the VPS may be encoded to include ageneral HRD parameters (general_hrd_parameters) syntax structure thatprovides/contains HRD parameters that apply to all OLSs specified by theVPS. The HRD parameters can be used to configure the HRD to performperformance tests on each OLS. For example, the HRD parameters mayindicate various delivery schedules that should be used by a HRD whenperforming conformance tests. As such, the presence of the HRDparameters in the bitstream indicates a decoder is capable of decodingthe bitstream according to a delivery schedule.

At step 1005, the HRD sequentially selects each operation point (OP) ofeach OLS as a targetOp. This can be done by selecting a target OLS withan opOlsIdx and a highest opTid, for example where opTid indicates atemporal frame rate associated with a layer/sublayer.

At step 1007, the HRD performs a set of bitstream conformance tests ateach OP of each OLS as specified by the VPS (e.g., as selected at step1005). This allows the HRD to test each OP for conformance. Accordingly,the HRD tests each OLS for conformance to standards. However, the HRDmay omit global conformance tests to the encoded bitstream orconformance tests to representations that can be output from the OLSs.The bitstream and the outputs are tested for conformance as part of theOLS conformance testing process. Hence, redundant conformance testingcan be avoided. Further, fewer conformance tests can be supported byfewer HRD parameters. Hence, applying conformance tests to only the OLSsreduces the number of HRD parameters in the VPS, and therefore reducesthe size of the bitstream encoded at steps 1001 and 1003. It should benoted that the HRD may operate on the same processor as the encoder. Inanother example, the HRD may operate on a processor in the same chassisas the encoder. In another example, the HRD may operate on a processorin the same network as the encoder.

At step 1009, the encoder stores the bitstream in memory forcommunication toward a decoder.

FIG. 11 is a flowchart of an example method 1100 of decoding a videosequence that was subjected to bitstream conformance tests for an OLS,for example by a HRD operating on an encoder, such as HRD 500. Method1100 may be employed by a decoder, such as a codec system 200, a decoder400, and/or a video coding device 900 when performing method 100.Further, method 1100 may operate on a bitstream, such as bitstream 800,which includes a multi-layer video sequence 600 and/or a multi-layervideo sequence 700.

Method 1100 may begin when a decoder begins receiving a bitstream ofcoded data representing a multi-layer video sequence, for example as aresult of method 1000. At step 1101, the decoder receives a bitstreamcomprising one or more OLSs. Each OLS is a set of layers for which oneor more of the layers are specified as output layers. The bitstream mayalso comprise a VPS specifying the OLSs. The VPS in the bitstream mayinclude a numoutput_layer_sets_minus1 plus one that specifies a totalnumber of OLSs specified by the VPS. Also, the VPS may include ageneral_hrd_parameters syntax structure that provides/contains HRDparameters that apply to all OLSs specified by the VPS. The presence ofthe HRD parameters in the bitstream indicates the decoder is capable ofdecoding the bitstream according to a delivery schedule (e.g., asspecified in the HRD parameters). The bitstream, as received, has beenchecked by a set of bitstream conformance tests for testing conformanceof each OP of each OLS specified by the VPS. Specifically, the set ofbitstream conformance tests are performed by a HRD operating on anencoder. For example, each OP is selected as a targetOp based on atarget OLS with a opOlsIdx and a highest opTid.

At step 1103, the decoder can decode a picture from the OLSs, forexample as part of a sublayer representation. The decoder can thenforward the picture for display as part of a decoded video sequence atstep 1105.

FIG. 12 is a schematic diagram of an example system 1200 for coding avideo sequence to support performance of bitstream conformance tests foran OLS. System 1200 may be implemented by an encoder and a decoder suchas a codec system 200, an encoder 300, a decoder 400, and/or a videocoding device 900. Further, the system 1200 may employ a HRD 500 toperform conformance tests on a multi-layer video sequence 600, amulti-layer video sequence 700, and/or a bitstream 800. In addition,system 1200 may be employed when implementing method 100, 1000, and/or1100.

The system 1200 includes a video encoder 1202. The video encoder 1202comprises an encoding module 1203 for encoding a bitstream comprisingone or more OLSs. The encoding module 1203 is further for encoding intothe bitstream a VPS specifying the OLSs. The video encoder 1202 furthercomprises a HRD module 1205 for performing a set of bitstreamconformance tests at each OP of each OLS, as specified by the VPS, totest each OP for conformance. The video encoder 1202 further comprises astoring module 1206 for storing the bitstream for communication toward adecoder. The video encoder 1202 further comprises a transmitting module1207 for transmitting the bitstream toward a video decoder 1210. Thevideo encoder 1202 may be further configured to perform any of the stepsof method 1000.

The system 1200 also includes a video decoder 1210. The video decoder1210 comprises a receiving module 1211 for receiving a bitstreamcomprising one or more OLSs and a VPS specifying the OLSs, wherein thebitstream has been checked by a set of bitstream conformance tests thattest conformance of each operation point (OP) of each OLS specified bythe VPS. The video decoder 1210 further comprises a decoding module 1213for decoding a picture from the OLSs. The video decoder 1210 furthercomprises a forwarding module 1215 for forwarding the picture fordisplay as part of a decoded video sequence. The video decoder 1210 maybe further configured to perform any of the steps of method 1100.

A first component is directly coupled to a second component when thereare no intervening components, except for a line, a trace, or anothermedium between the first component and the second component. The firstcomponent is indirectly coupled to the second component when there areintervening components other than a line, a trace, or another mediumbetween the first component and the second component. The term “coupled”and its variants include both directly coupled and indirectly coupled.The use of the term “about” means a range including ±10% of thesubsequent number unless otherwise stated.

It should also be understood that the steps of the exemplary methods setforth herein are not necessarily required to be performed in the orderdescribed, and the order of the steps of such methods should beunderstood to be merely exemplary. Likewise, additional steps may beincluded in such methods, and certain steps may be omitted or combined,in methods consistent with various embodiments of the presentdisclosure.

While several embodiments have been provided in the present disclosure,it may be understood that the disclosed systems and methods might beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. For example, the variouselements or components may be combined or integrated in another systemor certain features may be omitted, or not implemented.

In addition, techniques, systems, subsystems, and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, components, techniques, ormethods without departing from the scope of the present disclosure.Other examples of changes, substitutions, and alterations areascertainable by one skilled in the art and may be made withoutdeparting from the spirit and scope disclosed herein.

What is claimed is:
 1. A method implemented by a decoder, the methodcomprising: receiving, by the decoder, a bitstream comprising one ormore output layer sets (OLSs) and a video parameter set (VPS) specifyingthe OLSs, wherein the bitstream results from a set of bitstreamconformance tests that test conformance of each operation point (OP) ofeach OLS specified by the VPS; and decoding, by the decoder, a picturefrom the OLSs.
 2. The method of claim 1, wherein a hypotheticalreference decoder (HRD) is used to check the bitstream with the set ofbitstream conformance tests.
 3. The method of claim 1, wherein the VPSincludes a total number of output layer sets syntax element thatspecifies a total number of OLSs specified by the VPS.
 4. The method ofclaim 1, wherein each OP is selected as an OP under test (targetOp) byselecting a target OLS with an OP OLS index (opOlsIdx) and a highest OPtemporal identifier value (opTid).
 5. The method of claim 1, whereineach OLS is a set of layers for which one or more of the layers arespecified as output layers.
 6. The method of claim 1, wherein the VPSincludes a general hypothetical reference decoder (HRD) parameterssyntax structure that provides HRD parameters that apply to all OLSsspecified by the VPS.
 7. The method of claim 6, wherein a presence ofthe HRD parameters indicates the decoder is capable of decoding thebitstream according to a delivery schedule.
 8. A method implemented byan encoder, the method comprising: encoding, by the encoder, a bitstreamcomprising one or more output layer sets (OLSs); encoding into thebitstream, by the encoder, a video parameter set (VPS) specifying theOLSs; and performing, by the encoder, a set of bitstream conformancetests at each operation point (OP) of each OLS, as specified by the VPS,to test each OP for conformance.
 9. The method of claim 8, wherein ahypothetical reference decoder (HRD) is used to check the bitstream withthe set of bitstream conformance tests.
 10. The method of claim 8,wherein the VPS includes a total number of output layer sets syntaxelement that specifies a total number of OLSs specified by the VPS. 11.The method of claim 8, further comprising selecting, by the encoder,each OP as an OP under test (targetOp) by selecting a target OLS with anOP OLS index (opOlsIdx) and a highest OP temporal identifier value(opTid).
 12. The method of claim 8, wherein each OLS is a set of layersfor which one or more of the layers are specified as output layers. 13.The method of claim 8, wherein the VPS includes a general hypotheticalreference decoder (HRD) parameters syntax structure that provides HRDparameters that apply to all OLSs specified by the VPS.
 14. The methodof claim 13, wherein a presence of the HRD parameters indicates adecoder is capable of decoding the bitstream according to a deliveryschedule.
 15. A video coding device comprising: a receiver configured toreceive a bitstream comprising one or more output layer sets (OLSs) anda video parameter set (VPS) specifying the OLSs, wherein the bitstreamresults from a set of bitstream conformance tests that test conformanceof each operation point (OP) of each OLS specified by the VPS; and aprocessor coupled to the receiver and configured to decode a picturefrom the OLSs.
 16. The video coding device of claim 15, wherein ahypothetical reference decoder (HRD) is used to check the bitstream withthe set of bitstream conformance tests.
 17. The video coding device ofclaim 15, wherein the VPS includes a total number of output layer setssyntax element that specifies a total number of OLSs specified by theVPS.
 18. The video coding device of claim 15, wherein each OP isselected as an OP under test (targetOp) by selecting a target OLS withan OP OLS index (opOlsIdx) and a highest OP temporal identifier value(opTid).
 19. The video coding device of claim 15, wherein each OLS is aset of layers for which one or more of the layers are specified asoutput layers.
 20. The video coding device of claim 15, wherein the VPSincludes a general hypothetical reference decoder (HRD) parameterssyntax structure that provides HRD parameters that apply to all OLSsspecified by the VPS.